patch 8.2.4149: test override not restored, autocommand left behind

Problem:    Test override not restored, autocommand left behind.
Solution:   Correct restoring test override.  Delete autocommand afterwards.
diff --git a/src/testdir/test_autocmd.vim b/src/testdir/test_autocmd.vim
index 1fc960f..1ecb883 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
Binary files differ
diff --git a/src/testdir/test_mapping.vim b/src/testdir/test_mapping.vim
index 69de22b..aae3444 100644
--- a/src/testdir/test_mapping.vim
+++ b/src/testdir/test_mapping.vim
@@ -1453,6 +1453,7 @@
 
   nunmap <F3>
   unlet b:result
+  autocmd! CmdlineEnter
 endfunc
 
 " Test for using <script> with a map to remap characters in rhs