twister: remove spurious quoting of EXTRA_xFLAGS=-Werror

Testing shows cmake is invoked directly, not through a shell.

Fixes commit 5092541e2b59 ("sanitycheck: disable erroring on warnings").
Note EXTRA_AFLAGS was quoted only on the left side!

Signed-off-by: Marc Herbert <marc.herbert@intel.com>
1 file changed