patch 8.1.2230: MS-Windows: testing external commands can be improved

Problem:    MS-Windows: testing external commands can be improved.
Solution:   Adjust tests, remove duplicate test. (closes #4928)
diff --git a/src/testdir/test_normal.vim b/src/testdir/test_normal.vim
index da9c004..b37f613 100644
--- a/src/testdir/test_normal.vim
+++ b/src/testdir/test_normal.vim
@@ -408,8 +408,7 @@
 
   if executable('echo')
     " Test expand(`...`) i.e. backticks command expansion.
-    " MS-Windows has a trailing space.
-    call assert_match('^abcde *$', expand('`echo abcde`'))
+    call assert_equal('abcde', expand('`echo abcde`'))
   endif
 
   " Test expand(`=...`) i.e. backticks expression expansion