gdb/gdbarch: remove the predicate function for gdbarch_register_type

gdb/gdbarch: remove the predicate function for gdbarch_register_type

I don't believe that the gdbarch_register_type_p predicate is called
anywhere in GDB, and the gdbarch_register_type function is called
without checking the gdbarch_register_type_p predicate function
everywhere it is used, for example in
init_regcache_descr (regcache.c).

My claim is that the gdbarch_register_type function is required for
every architecture, and GDB will not work if this function is not
supplied.

And so, in this commit, I remove the 'predicate=True' from
gdbarch-components.py for the 'register_type' field, and regenerate
the gdbarch files.

There should be no user visible changes after this commit.