Revert "include/spinlock: explicit casts for C++ compilation"

This reverts commit 8698ada953.
Concurrency Kit uses idiomatic C99+.

include/spinlock/clh.h

@@ -78,7 +78,7 @@ ck_spinlock_clh_lock(struct ck_spinlock_clh **queue, struct ck_spinlock_clh *thr
 	 * Mark current request as last request. Save reference to previous
 	 * request.
 	 */
-	previous = CK_CPP_CAST(struct ck_spinlock_clh *, ck_pr_fas_ptr(queue, thread));
+	previous = ck_pr_fas_ptr(queue, thread);
 	thread->previous = previous;
 
 	/* Wait until previous thread is done with lock. */

include/spinlock/hclh.h

@@ -88,7 +88,7 @@ ck_spinlock_hclh_lock(struct ck_spinlock_hclh **glob_queue,
 	ck_pr_fence_store_atomic();
 
 	/* Mark current request as last request. Save reference to previous request. */
-	previous = CK_CPP_CAST(struct ck_spinlock_hclh *, ck_pr_fas_ptr(local_queue, thread));
+	previous = ck_pr_fas_ptr(local_queue, thread);
 	thread->previous = previous;
 
 	/* Wait until previous thread from the local queue is done with lock. */
@@ -107,7 +107,7 @@ ck_spinlock_hclh_lock(struct ck_spinlock_hclh **glob_queue,
 
 	/* Now we need to splice the local queue into the global queue. */
 	local_tail = ck_pr_load_ptr(local_queue);
-	previous = CK_CPP_CAST(struct ck_spinlock_hclh *, ck_pr_fas_ptr(glob_queue, local_tail));
+	previous = ck_pr_fas_ptr(glob_queue, local_tail);
 
 	ck_pr_store_uint(&local_tail->splice, true);
 

include/spinlock/mcs.h

@@ -97,7 +97,7 @@ ck_spinlock_mcs_lock(struct ck_spinlock_mcs **queue,
 	 * returns NULL, it means the queue was empty. If the queue was empty,
 	 * then the operation is complete.
 	 */
-	previous = CK_CPP_CAST(struct ck_spinlock_mcs *, ck_pr_fas_ptr(queue, node));
+	previous = ck_pr_fas_ptr(queue, node);
 	if (previous != NULL) {
 		/*
 		 * Let the previous lock holder know that we are waiting on