Reduce usage of TURN_NO_PROMETHEUS

[eakraly]

TURN_NO_PROMETHEUS is defined when prometheus libraries are not present and any prometheus functionality must be disabled

While all above is correct, it does not require ifdef-ing out all related code. For example, prometheus related fields in turn_params do not need to be compiled out. Same for certain function parameters.

This PR reduces amount of places in code where TURN_NO_PROMETHEUS is used to make code simpler by moving as much usage of this define into prom_server.h/c files and compiling them unconditionally.

• Always compile/link prom_server.c
• Move many TURN_NO_PROMETHEUS decisions into prom_server.c