Revert "include: Add dummy field for Rust as well as CPP"

This reverts commit 2046760.

Put these back so we get the zero element structures when using just
rust and not CPP.  A subsequent patch will suppress the warning.

Signed-off-by: David Brown <[email protected]>

Author: d3zd3z

include/zephyr/kernel/thread.h

@@ -237,7 +237,7 @@ typedef struct k_thread_runtime_stats {
 	uint64_t idle_cycles;
 #endif /* CONFIG_SCHED_THREAD_USAGE_ALL */
 
-#if (defined(__cplusplus) || CONFIG_RUST) && !defined(CONFIG_SCHED_THREAD_USAGE) &&	\
+#if defined(__cplusplus) && !defined(CONFIG_SCHED_THREAD_USAGE) &&                                 \
 	!defined(CONFIG_SCHED_THREAD_USAGE_ANALYSIS) && !defined(CONFIG_SCHED_THREAD_USAGE_ALL)
 	/* If none of the above Kconfig values are defined, this struct will have a size 0 in C
 	 * which is not allowed in C++ (it'll have a size 1). To prevent this, we add a 1 byte dummy

include/zephyr/spinlock.h

@@ -78,7 +78,7 @@ struct k_spinlock {
 #endif /* CONFIG_SPIN_LOCK_TIME_LIMIT */
 #endif /* CONFIG_SPIN_VALIDATE */
 
-#if (defined(CONFIG_CPP) || defined(CONFIG_RUST)) && !defined(CONFIG_SMP) && \
+#if defined(CONFIG_CPP) && !defined(CONFIG_SMP) && \
 	!defined(CONFIG_SPIN_VALIDATE)
 	/* If CONFIG_SMP and CONFIG_SPIN_VALIDATE are both not defined
 	 * the k_spinlock struct will have no members. The result