Remove staging from commit workflow in the Web IDE

What does this MR do?

Removes staging from the commit workflow in the Web IDE. Issue: #196609 (closed)

Note: This MR only removes staging from the workflow in the view in the spirit of shipping the user facing change faster. Internally, everything is still staged by default before committing. Removing all staging functionality internally is a massive undertaking, and it would be advisable to do it over multiple releases as multiple tech debt tasks. As an example, if you search for the word 'stage' in the ide folder, there are over 750 occurrences, all of which will need to be removed or replaced as a part of the tech debt.

I will create follow up issues to clear the tech debt that arises as a result of removal of this feature.

Screenshots

Description	Before	After
Modification tooltip + footer text below commit button
New file tooltip
Collapsed folder tooltip
Changes tab
Discard all warning

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability 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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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