Apply suggestions from code review

Co-authored-by: Erik Krogh Kristensen <erik-krogh@github.com>

Author: atorralba

ql/ql/src/queries/style/OmittableExists.ql

@@ -15,7 +15,7 @@ where
   existsArgument = any(Exists e).getAnArgument() and
   use = unique( | | existsArgument.getAnAccess()) and
   exists(Call c, int argPos | c.getArgument(argPos) = use |
-    not existsArgument.getType().getASuperType+() = c.getTarget().getParameterType(argPos)
+    existsArgument.getType() = c.getTarget().getParameterType(argPos).getASuperType*()
   )
-select existsArgument, "This exists argument can be omitted by using a don't-care expression $@.",
+select existsArgument, "This exists variable can be omitted by using a don't-care expression $@.",
   use, "in this argument"

ql/ql/test/queries/style/OmittableExists/OmittableExists.expected

@@ -1 +1 @@
-| Test.qll:10:10:10:14 | i | This exists argument can be omitted by using a don't-care expression $@. | Test.qll:10:29:10:29 | i | in this argument |
+| Test.qll:10:10:10:14 | i | This exists variable can be omitted by using a don't-care expression $@. | Test.qll:10:29:10:29 | i | in this argument |