gdbarch.sh: Remove commented out TARGET_CHAR_BIT definition

gdbarch.sh: Remove commented out TARGET_CHAR_BIT definition

As Pedro commented on the patch "Change field separator in gdbarch.sh",
this commented out definition is probably not useful and should be
removed.  It has been commented out for basically forever, and it
probably serves the same intent as addressable_memory_unit_size.

gdb/ChangeLog:

	* gdbarch.sh: Remove commented out definition of
	TARGET_CHAR_BIT.
	* gdbarch.h: Re-generate.