oldtest: windows: revert setting shellslash individually (#10189)

* Revert "oldtests: win: shellslash for cdpath,tags,:find"

This reverts commit 6245b4873d.

* Revert "oldtests: set shellslash for ":cd" test"

This reverts commit eba1ebafe5.

* Revert "oldtests: set shellslash in Test_shellescape()"

This reverts commit e428fc4b52.

* Revert "fixup! vim-patch:8.0.1782: no simple way to label quickfix entries"

This reverts commit ac1fbc2860.

* Revert "test/old: pass Test_statusline on Windows"

This reverts commit 6efa3bff09.

* Revert "oldtests: set shellslash for Test_non_zero_arg"

This reverts commit 42e1e2495c.

* Revert "oldtests: set shellslash in Test_true_false_arg()"

This reverts commit 8bd194f98a.

* Remove unnecessary set shellslash

Since #10679 no longer requires individual set shellslash, it is removed.


Co-Authored-By: erw7 <erw7.github@gmail.com>

src/nvim/testdir/test_quickfix.vim

@@ -139,8 +139,6 @@ func XlistTests(cchar)
 	      \ ' 5:50 col 25  55: one'], l)
 
   " Test for module names, one needs to explicitly set `'valid':v:true` so
-  let save_shellslash = &shellslash
-  set shellslash
   call g:Xsetlist([
         \ {'lnum':10,'col':5,'type':'W','module':'Data.Text','text':'ModuleWarning','nr':11,'valid':v:true},
         \ {'lnum':20,'col':10,'type':'W','module':'Data.Text','filename':'Data/Text.hs','text':'ModuleWarning','nr':22,'valid':v:true},
@@ -149,7 +147,6 @@ func XlistTests(cchar)
   call assert_equal([' 1 Data.Text:10 col 5 warning  11: ModuleWarning',
         \ ' 2 Data.Text:20 col 10 warning  22: ModuleWarning',
         \ ' 3 Data/Text.hs:30 col 15 warning  33: FileWarning'], l)
-  let &shellslash = save_shellslash
 
   " Error cases
   call assert_fails('Xlist abc', 'E488:')