Remove unnecessary util.callable usage

Fixes: #4850

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### Description
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Removes usage of `util.callable`.

### Checklist
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This pull request is:

- [ ] A documentation / typographical error fix
	- Good to go, no issue or tests are needed
- [x] A short code fix
	- please include the issue number, and create an issue if none exists, which
	  must include a complete example of the issue.  one line code fixes without an
	  issue and demonstration will not be accepted.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.   one line code fixes without tests will not be accepted.
- [ ] A new feature implementation
	- please include the issue number, and create an issue if none exists, which must
	  include a complete example of how the feature would look.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.

**Have a nice day!**

Closes: #4851
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/4851
Pull-request-sha: a0ccdff2cb74f5e944d8baccc269c382b591c8e2

Change-Id: I79918f44becbc5dbefdc7ff65128695c1cabed1d

1 files changed, 1 insertions, 1 deletions

diff --git a/lib/sqlalchemy/sql/ddl.py b/lib/sqlalchemy/sql/ddl.py
index ef6614b61..48d4bc9dc 100644
--- a/lib/sqlalchemy/sql/ddl.py
+++ b/lib/sqlalchemy/sql/ddl.py
@@ -258,7 +258,7 @@ class DDLElement(roles.DDLRole, Executable, _DDLCompiles):
     def _check_ddl_on(self, on):
         if on is not None and (
             not isinstance(on, util.string_types + (tuple, list, set))
-            and not util.callable(on)
+            and not callable(on)
         ):
             raise exc.ArgumentError(
                 "Expected the name of a database dialect, a tuple "