kernel: Clean-up lingering code coverage exclusion flag

Remove LCOV_EXCL_STOP flag as LCOV_EXCL_START was removed in a previous
commit.  This causes a gcov compilation error.

Signed-off-by: Al Semjonovs <asemjonovs@google.com>

Author: asemjonovs

kernel/init.c

@@ -187,8 +187,6 @@ extern volatile uintptr_t __stack_chk_guard;
 #endif /* CONFIG_STACK_CANARIES_TLS */
 #endif /* CONFIG_REQUIRES_STACK_CANARIES */
 
-/* LCOV_EXCL_STOP */
-
 __pinned_bss
 bool z_sys_post_kernel;