linker: Remove unused (OPTIONAL) from linker scripts

(OPTIONAL) was a vestiage from the initial import of the Zephyr code
base and we dont utilize it with the GNU linker.  Additionally, the way
(OPTIONAL) gets defined to nothing creates a linker script that lld
(from llvm) doesn't like.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
11 files changed