*/*: Remove many function pointer casts.

In C it is undefined behavior to call a function through a function pointer
of a different type.  This is now detected by the Control Flow Integrity
Sanitizer.  All known issues have already been fixed.  Prevent any
accidental re-introduction by removing function pointer casts when defining
services.  The services will call the service functions through the function
pointers on the service.  As a result the functions must have the same type
so there should be no need to cast.  Removing the casts allows compilers to
warn about assignment to an incompatible function pointer type.