flash/nor/at91sam3: remove sam3_page_write_opcodes

Apparently this helper was never actually used, and current clang
produces an unused const variable warning, so it's breaking the build.

Change-Id: Ib088bef5e9c0a48942c1d417d46f738469ee7e28
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2076


Tested-by: jenkins
Reviewed-by: Xiaofan <xiaofanc@gmail.com>