arch/Kconfig: Drop always true condition from RANDOMIZE_KSTACK_OFFSET

Now that the minimum supported version of LLVM for building the kernel
has been bumped to 15.0.0, the second depends line in
RANDOMIZE_KSTACK_OFFSET is always true, so it can be removed.

Reviewed-by: Kees Cook <kees@kernel.org>
Link: https://lore.kernel.org/r/20250821-bump-min-llvm-ver-15-v2-2-635f3294e5f0@kernel.org


Signed-off-by: Nathan Chancellor <nathan@kernel.org>