Remove unused request form processing for bearer tokens and associated dead frontend code

[jacobshandling]

Goal

User story
As a Fleet developer,
I want to increase the signal/noise ratio of the codebase
so that I can more quickly and deeply grok it.

While making this update, I noticed this code that oddly looks for a bearer token in a POST request's body. Doing some spelunking with @gillespi314, we found it was introduced here to handle this endpoint , which no longer exists in the backend and which has some related dead frontend code

It seems the parsing of the request form to find a bearer token is both no longer used and an atypical pattern, and should be removed

[jacobshandling]

@lucasmrod @iansltx, would you agree we can/should remove this request body parsing?

[iansltx]

@jacobshandling I'll approve the PR when it shows up.