In lab assistant sign-in, only include current options

[kavigupta]

In the lab assistant sign-in, every possible combination of type/TA options is shown, an AI can choose, for example, Lab / Kavi during my office hours, even though I am not teaching a lab during that time.

It might be helpful if OK only showed current options. An "other" field would also be required if, for example, someone was substituting for someone else.

[knrafto]

Moving this to https://github.com/Cal-CS-61A-Staff/Check-In