Remove the display of known MCU names from the MSP430 port of GAS.

Remove the display of known MCU names from the MSP430 port of GAS.

New MSP430 MCU parts are being created by TI all the time and the
list is basically always out of date.  Instead any name will be
accepted by the -mmcu= command line option.  ISA selection is now
based upon the -mcpu= command line option, just as is done for GCC.

gas/ChangeLog
	* config/tc-msp430.c (show_mcu_list): Delete.
	(md_parse_option): Accept any MCU name.  Accept several more
	variants for the -mcpu option.
	(md_show_usage): Do not call show_mcu_list.