lint: Migrate typing.Text check to semgrep.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

tools/linter_lib/custom_check.py

@@ -360,16 +360,6 @@ python_rules = RuleList(
          'bad_lines': ['desc: Optional[Text] = models.TextField()',
                        'stream: Optional[Stream] = models.ForeignKey(Stream, on_delete=CASCADE)'],
          },
-        {'pattern': r'[\s([]Text([^\s\w]|$)',
-         'exclude': {
-             # We are likely to want to keep these dirs Python 2+3 compatible,
-             # since the plan includes extracting them to a separate project eventually.
-             'tools/lib',
-             # TODO: Update our migrations from Text->str.
-             'zerver/migrations/',
-         },
-         'description': "Now that we're a Python 3 only codebase, we don't need to use typing.Text. Please use str instead.",
-         },
         {'pattern': 'exit[(]1[)]',
          'include_only': {"/management/commands/"},
          'description': 'Raise CommandError to exit with failure in management commands',