Changed error handling for some SQL errors

[Xemdo]

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Problem/Feature

sqlite3 package was causing me some issues on vscode because of golang/vscode-go#2988, so while waiting for that to resolve I figured I'd remove the error old SQL error handling here.

It seemed like it wasn't necessary as it was only used by one Mock API call to see if the Category ID existed in the database, which I replaced with an additional database call.

Description of Changes:

• Removed old SQL error handling
• Changed PATCH /mock/channels to check if the game category exists when its being updated

Checklist

• My code follows the Contribution Guide
• I have self-reviewed the changes being requested
• I have made comments on pieces of code that may be difficult to understand for other editors
• I have updated the documentation (if applicable)