Fix hash comment removal in GraphQL schemas

The regex used to remove hash comments originally used the re.MULTILINE
flag. Now that that flag is gone, the '$' in the regex no longer makes
sense (it only matches the end of the file). The regex also had a
dangling '\1' backreference that has been removed as well.

I recently federated some additional GraphQL types and converted
docstrings to hash comments in the process, at which point I noticed the
linter wasn't removing comments as expected.

Issue: none

Test plan:
ka-lint services/*/*.graphql

Auditors: csilvers

linters.py

@@ -900,7 +900,7 @@ def process(self, f, contents_of_f):
         contents_without_comments = re.sub(
             r'""".*?"""', "", contents_of_f, flags=re.DOTALL)
         contents_without_comments = re.sub(
-            r'#.*$', r"\1", contents_without_comments)
+            r'#.*', '', contents_without_comments)
 
         # Now find undefined types and add them in.
         new_type_re = re.compile(