testsuite: Ignore BASH_REMATCH in env unmodified check.

_init_completion uses =~ now so it's going to change just about everywhere.

test/lib/completions/ant.exp

@@ -6,7 +6,6 @@ proc setup {} {
 proc teardown {} {
     assert_env_unmodified {
         /OLDPWD=/d
-        /BASH_REMATCH=/d
     }
 }
 

test/lib/library.sh

@@ -22,6 +22,8 @@ diff_env() {
         /[<>] _=/d
 # Remove PPID bash variable
         /[<>] PPID=/d
+# Remove BASH_REMATCH bash variable
+        /[<>] BASH_REMATCH=/d
         $3"
 } # diff_env()