patch 9.0.0719: 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_search_stat.vim b/src/testdir/test_search_stat.vim
index 71e050c..b8509ba 100644
--- a/src/testdir/test_search_stat.vim
+++ b/src/testdir/test_search_stat.vim
@@ -287,7 +287,7 @@
     set hlsearch
     set laststatus=2 statusline+=%{TestSearchCount()}
   END
-  call writefile(lines, 'Xsearchstatusline')
+  call writefile(lines, 'Xsearchstatusline', 'D')
   let buf = RunVimInTerminal('-S Xsearchstatusline', #{rows: 10})
   call TermWait(buf)
   call term_sendkeys(buf, "/something")
@@ -295,7 +295,6 @@
 
   call term_sendkeys(buf, "\<Esc>")
   call StopVimInTerminal(buf)
-  call delete('Xsearchstatusline')
 endfunc
 
 func Test_search_stat_foldopen()
@@ -309,7 +308,7 @@
     call cursor(1,1)
     norm n
   END
-  call writefile(lines, 'Xsearchstat1')
+  call writefile(lines, 'Xsearchstat1', 'D')
 
   let buf = RunVimInTerminal('-S Xsearchstat1', #{rows: 10})
   call VerifyScreenDump(buf, 'Test_searchstat_3', {})
@@ -321,7 +320,6 @@
   call VerifyScreenDump(buf, 'Test_searchstat_3', {})
 
   call StopVimInTerminal(buf)
-  call delete('Xsearchstat1')
 endfunc
 
 func! Test_search_stat_screendump()
@@ -338,7 +336,7 @@
     call cursor(1,1)
     norm n
   END
-  call writefile(lines, 'Xsearchstat')
+  call writefile(lines, 'Xsearchstat', 'D')
   let buf = RunVimInTerminal('-S Xsearchstat', #{rows: 10})
   call VerifyScreenDump(buf, 'Test_searchstat_1', {})
 
@@ -347,7 +345,6 @@
   call VerifyScreenDump(buf, 'Test_searchstat_2', {})
 
   call StopVimInTerminal(buf)
-  call delete('Xsearchstat')
 endfunc
 
 func Test_search_stat_then_gd()
@@ -358,7 +355,7 @@
     set shortmess-=S
     set hlsearch
   END
-  call writefile(lines, 'Xsearchstatgd')
+  call writefile(lines, 'Xsearchstatgd', 'D')
 
   let buf = RunVimInTerminal('-S Xsearchstatgd', #{rows: 10})
   call term_sendkeys(buf, "/dog\<CR>")
@@ -368,7 +365,6 @@
   call VerifyScreenDump(buf, 'Test_searchstatgd_2', {})
 
   call StopVimInTerminal(buf)
-  call delete('Xsearchstatgd')
 endfunc
 
 func Test_search_stat_and_incsearch()
@@ -392,7 +388,7 @@
 
     set tabline=%!MyTabLine()
   END
-  call writefile(lines, 'Xsearchstat_inc')
+  call writefile(lines, 'Xsearchstat_inc', 'D')
 
   let buf = RunVimInTerminal('-S Xsearchstat_inc', #{rows: 10})
   call term_sendkeys(buf, "/abc")
@@ -411,7 +407,6 @@
   call TermWait(buf)
 
   call StopVimInTerminal(buf)
-  call delete('Xsearchstat_inc')
 endfunc