Remove unneeded type assertions

[Timothy-Gonzalez]

Code like:

const requestBody: SubscribeRequest = request.body as SubscribeRequest;
const emailAddress: string | undefined = requestBody.emailAddress;
const isStaff: boolean = hasStaffPerms(payload);

can be simplified to:

const requestBody = request.body as SubscribeRequest;
const emailAddress = requestBody.emailAddress;
const isStaff = hasStaffPerms(payload);

This makes TypeScript needlessly verbose and ruins the point of typescript in the first place - safety without the pain of it.

Most modern editors will show the inferred types if you hover over the variable or they can be explicitly shown if you want.

This is another issue that will conflict with anything, but this code is ugly and makes typescript more painful then it needs to be.

We can probably use something like no-unnecessary-type-assertion to fix this going forward.