b43: Remove unused phy_a code

gcc-6 reports the following error with -Werror=unused-const-variable.

drivers/net/wireless/broadcom/b43/phy_a.c:576:40: error:
	'b43_phyops_a' defined but not used

Per Michael Büsch: "All a-phy code is usused", so remove it all,
and move the remaining Type-G initialization code into phy_g.c.

Reported-by: Fengguang Wu <fengguang.wu@intel.com> [0-day test robot]
Cc: Michael Büsch <m@bues.ch>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>