Get rid of symfony-exceptions.patch

[rmunn]

Fixes #1814

Description

We can finally get rid of this hacky "patch a vendor library in place" solution now that PHP exceptions are deriving from the Exception class rather than the Error class.

Screenshots

None; no behavior change.

Checklist

• [X] I have labeled my PR with: bug, feature, engineering, security fix or testing
• [X] I have performed a self-review of my own code
• [X] I have reviewed the title & description of this PR which I will use as the squashed PR commit message
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have enabled auto-merge (optional)

Testing

Testers, use the following instructions against our staging environment. Post your findings as a comment and include any meaningful screenshots, etc.

Describe how to verify your changes and provide any necessary test data.

• Run make and make sure the site still works.
• If MongoDB auth is enabled, try changing the MONGODB_PASS env var to an incorrect value to see an exception when you try to go to http://localhost:8080/auth/login

[github-actions[bot]]

Unit Test Results

362 tests   362 :white_check_mark:  13s :stopwatch:  37 suites    0 :zzz:   1 files      0 :x:

Results for commit e685f1df.

:recycle: This comment has been updated with latest results.

[rmunn]

@megahirt - Done. I've brought the patch file back, and simply commented out the lines in the Dockerfile that would apply it. So if this exception-swallowing behavior comes back in the future, it'll be obvious from reading the Dockerfile what to do about it.