feature-arm-thumb.inc: drop 'no-thumb-interwork' tuning feature

feature-arm-thumb.inc: drop 'no-thumb-interwork' tuning feature

Interworking is required for ARM EABI, so attempting to disable it
via a tuning feature no longer makes sense (support for ARM OABI was
deprecated in gcc 4.7). We can drop '-mthumb-interwork' from
TUNE_CCARGS for the same reason.

(From OE-Core rev: d942f94de8966c839209e8c9a632351d108852c4)

Signed-off-by: Andre McCurdy <armccurdy@gmail.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>