Removed the MacVim checks for test_filechanged.vim

The GUI dialog bug has been fixed in Vim by not running
Test_file_changed_dialog() when GUI is running, so no need to put
MacVim-specific check for that.

src/testdir/test_filechanged.vim

@@ -1,11 +1,5 @@
 " Tests for when a file was changed outside of Vim.
 
-if has('gui_macvim') && has('gui_running')
-  " MacVim's currently stalls and never returns when the GUI vesion is run in
-  " CI. Disable these tests for now before a more proper fix is implemented.
-  finish
-endif
-
 func Test_FileChangedShell_reload()
   if !has('unix')
     return