Use same hash function for hashfn_profiler as for hash_string etc.

Use same hash function for hashfn_profiler as for hash_string etc.

* fns.c (SXHASH_COMBINE): Remove.  All uses replaced by sxhash_combine.
* lisp.h (sxhash_combine): New inline function, with the contents
of the old SXHASH_COMBINE.
* profiler.c (hashfn_profiler): Use it, instead of having a
special hash function containing a comparison that always yields 1.