Mild simplifications and improvements to bank logic

What has been done in this MR?

• Removed some unnecessary complexity from bank logic
• Replaced some incorrect ways of doing things with the correct ways of doing things
• Properly track the set bank tab and set the corresponding varbit (old bank code didn't do this, and when the very incorrect tab update code modified varp 1248 without this varbit properly set, it would cause the annoying search-screen-showing-up-when-it-shouldn't bug.)

What should testers check?

• Bank feels a bit more responsive (useless delays removed and overall functionality brought inline with CS2 expectations)
• Bank still functions at least as correctly as it did before
• Ideally, bank no longer stays a state behind at all times (I couldn't verify this, as I can't reproduce the bug locally, though I suspect these changes should help.)

• I have tested these changes thoroughly.

• I used the relevant Zaros tool for any JSON edits where possible, and have attached screenshots of any changes.