Remove always_populate_raw_post_data requirements check, which might be incorrect

This may need more research, but based on discussion in #2931883: Unneeded always_populate_raw_post_data requirements check while on CLI the REST module's always_populate_raw_post_data requirement check is possibly not necessary.

And at least, it appears to enforce a solution to the problem that may not be the best one (see #2931883-11: Unneeded always_populate_raw_post_data requirements check while on CLI).