patch 9.0.0619: too many delete() calls in tests

Problem:    Too many delete() calls in tests.
Solution:   Use deferred delete where possible.
diff --git a/src/testdir/test_highlight.vim b/src/testdir/test_highlight.vim
index ef9c70e..26426e0 100644
--- a/src/testdir/test_highlight.vim
+++ b/src/testdir/test_highlight.vim
@@ -540,7 +540,7 @@
   call writefile([
 	\ 'set cul rnu',
 	\ 'call setline(1, ["","1","2","3",""])',
-	\ ], 'Xtest_cursorline_yank')
+	\ ], 'Xtest_cursorline_yank', 'D')
   let buf = RunVimInTerminal('-S Xtest_cursorline_yank', {'rows': 8})
   call TermWait(buf)
   call term_sendkeys(buf, "Gy3k")
@@ -551,7 +551,6 @@
 
   " clean up
   call StopVimInTerminal(buf)
-  call delete('Xtest_cursorline_yank')
 endfunc
 
 " test for issue #4862
@@ -580,7 +579,7 @@
   call writefile([
 	\ 'set cul',
 	\ 'call setline(1, repeat(["abc"], 50))',
-	\ ], 'Xtest_cursorline_with_visualmode')
+	\ ], 'Xtest_cursorline_with_visualmode', 'D')
   let buf = RunVimInTerminal('-S Xtest_cursorline_with_visualmode', {'rows': 12})
   call TermWait(buf)
   call term_sendkeys(buf, "V\<C-f>kkkjk")
@@ -589,7 +588,6 @@
 
   " clean up
   call StopVimInTerminal(buf)
-  call delete('Xtest_cursorline_with_visualmode')
 endfunc
 
 func Test_cursorcolumn_insert_on_tab()
@@ -600,7 +598,7 @@
     set cursorcolumn
     call cursor(2, 2)
   END
-  call writefile(lines, 'Xcuc_insert_on_tab')
+  call writefile(lines, 'Xcuc_insert_on_tab', 'D')
 
   let buf = RunVimInTerminal('-S Xcuc_insert_on_tab', #{rows: 8})
   call TermWait(buf)
@@ -619,7 +617,6 @@
   call VerifyScreenDump(buf, 'Test_cursorcolumn_insert_on_tab_2', {})
 
   call StopVimInTerminal(buf)
-  call delete('Xcuc_insert_on_tab')
 endfunc
 
 func Test_cursorcolumn_callback()
@@ -637,14 +634,13 @@
 
       call timer_start(300, 'Func')
   END
-  call writefile(lines, 'Xcuc_timer')
+  call writefile(lines, 'Xcuc_timer', 'D')
 
   let buf = RunVimInTerminal('-S Xcuc_timer', #{rows: 8})
   call TermWait(buf, 310)
   call VerifyScreenDump(buf, 'Test_cursorcolumn_callback_1', {})
 
   call StopVimInTerminal(buf)
-  call delete('Xcuc_timer')
 endfunc
 
 func Test_wincolor()
@@ -663,7 +659,7 @@
 	call prop_add(6, 12, {"type": "foo", "end_col": 15})
 	/here
   END
-  call writefile(lines, 'Xtest_wincolor')
+  call writefile(lines, 'Xtest_wincolor', 'D')
   let buf = RunVimInTerminal('-S Xtest_wincolor', {'rows': 8})
   call TermWait(buf)
   call term_sendkeys(buf, "2G5lvj")
@@ -674,7 +670,6 @@
   " clean up
   call term_sendkeys(buf, "\<Esc>")
   call StopVimInTerminal(buf)
-  call delete('Xtest_wincolor')
 endfunc
 
 func Test_wincolor_listchars()
@@ -689,7 +684,7 @@
 	call matchadd('Conceal', 'text')
 	normal 2G5zl
   END
-  call writefile(lines, 'Xtest_wincolorlcs')
+  call writefile(lines, 'Xtest_wincolorlcs', 'D')
   let buf = RunVimInTerminal('-S Xtest_wincolorlcs', {'rows': 8})
 
   call VerifyScreenDump(buf, 'Test_wincolor_lcs', {})
@@ -697,7 +692,6 @@
   " clean up
   call term_sendkeys(buf, "\<Esc>")
   call StopVimInTerminal(buf)
-  call delete('Xtest_wincolorlcs')
 endfunc
 
 func Test_colorcolumn()
@@ -714,14 +708,13 @@
 	wincmd w
 	buf X
   END
-  call writefile(lines, 'Xtest_colorcolumn')
+  call writefile(lines, 'Xtest_colorcolumn', 'D')
   let buf = RunVimInTerminal('-S Xtest_colorcolumn', {'rows': 10})
   call term_sendkeys(buf, ":\<CR>")
   call VerifyScreenDump(buf, 'Test_colorcolumn_1', {})
 
   " clean up
   call StopVimInTerminal(buf)
-  call delete('Xtest_colorcolumn')
 endfunc
 
 func Test_colorcolumn_bri()
@@ -731,14 +724,13 @@
   let lines =<< trim END
 	call setline(1, 'The quick brown fox jumped over the lazy dogs')
   END
-  call writefile(lines, 'Xtest_colorcolumn_bri')
+  call writefile(lines, 'Xtest_colorcolumn_bri', 'D')
   let buf = RunVimInTerminal('-S Xtest_colorcolumn_bri', {'rows': 10,'columns': 40})
   call term_sendkeys(buf, ":set co=40 linebreak bri briopt=shift:2 cc=40,41,43\<CR>")
   call VerifyScreenDump(buf, 'Test_colorcolumn_2', {})
 
   " clean up
   call StopVimInTerminal(buf)
-  call delete('Xtest_colorcolumn_bri')
 endfunc
 
 func Test_colorcolumn_sbr()
@@ -748,14 +740,13 @@
   let lines =<< trim END
 	call setline(1, 'The quick brown fox jumped over the lazy dogs')
   END
-  call writefile(lines, 'Xtest_colorcolumn_srb')
+  call writefile(lines, 'Xtest_colorcolumn_srb', 'D')
   let buf = RunVimInTerminal('-S Xtest_colorcolumn_srb', {'rows': 10,'columns': 40})
   call term_sendkeys(buf, ":set co=40 showbreak=+++>\\  cc=40,41,43\<CR>")
   call VerifyScreenDump(buf, 'Test_colorcolumn_3', {})
 
   " clean up
   call StopVimInTerminal(buf)
-  call delete('Xtest_colorcolumn_srb')
 endfunc
 
 " This test must come before the Test_cursorline test, as it appears this