Further refine patch for commenting operator implementation functions.

Further refine patch for commenting operator implementation functions.

Instead of manually maintaining the "implementation of XXX operator"
comments in pg_proc.h, delete all those entries and let initdb create
them via a join.  To let initdb figure out which name to use when there
is a conflict, change the comments for deprecated operators to say they
are deprecated --- which seems like a good thing to do anyway.