Change security harness to rely on overcommit

What does this MR do?

Security harness relies on custom pre-push git hooks which conflicts with overcommit.

Overcommit is a much better tool for adding custom checks on git commands and can be used for many other checks. The existing security harness prevents the use of overcommit.

This MR proposes dropping the custom hook and relying on overcommit instead.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team