MSP430: Remove unused -md GAS option

The MSP430 GAS option "-md" is supposed to indicate that the CRT startup
code should copy data from ROM to RAM at startup. However, this option
has no effect; GAS handles the related behaviour automatically by
looking for the presence of certain symbols in the input file.

gas/ChangeLog:

	* config/tc-msp430.c (OPTION_MOVE_DATA): Remove.
	(md_parse_option): Remove case for OPTION_MOVE_DATA.
	(md_longopts): Remove "md" entry.
	(md_show_usage): Likewise.