MINOR: pools: drop the unused static history of artificially failed allocs

When building with DEBUG_FAIL_ALLOC we call a random generator to decide
whether the pool alloc should succeed or fail, and there was a preliminary
debugging mechanism to keep sort of a history of the previous decisions. But
it was never used, enforces a lock during the allocation, and forces to use
static variables, all of which are limiting the ability to pursue the pools
cleanups with no real benefit. Let's get rid of them now.
diff --git a/src/pool.c b/src/pool.c
index 0227f36..cdb3eef 100644
--- a/src/pool.c
+++ b/src/pool.c
@@ -655,16 +655,10 @@
 INITCALL1(STG_REGISTER, cli_register_kw, &cli_kws);
 
 #ifdef DEBUG_FAIL_ALLOC
-#define MEM_FAIL_MAX_CHAR 32
-#define MEM_FAIL_MAX_STR 128
-static int mem_fail_cur_idx;
-static char mem_fail_str[MEM_FAIL_MAX_CHAR * MEM_FAIL_MAX_STR];
-__decl_thread(static HA_SPINLOCK_T mem_fail_lock);
 
 int mem_should_fail(const struct pool_head *pool)
 {
 	int ret = 0;
-	int n;
 
 	if (mem_fail_rate > 0 && !(global.mode & MODE_STARTING)) {
 		int randnb = ha_random() % 100;
@@ -674,20 +668,6 @@
 		else
 			ret = 0;
 	}
-	HA_SPIN_LOCK(POOL_LOCK, &mem_fail_lock);
-	n = snprintf(&mem_fail_str[mem_fail_cur_idx * MEM_FAIL_MAX_CHAR],
-	    MEM_FAIL_MAX_CHAR - 2,
-	    "%d %.18s %d %d", mem_fail_cur_idx, pool->name, ret, tid);
-	while (n < MEM_FAIL_MAX_CHAR - 1)
-		mem_fail_str[mem_fail_cur_idx * MEM_FAIL_MAX_CHAR + n++] = ' ';
-	if (mem_fail_cur_idx < MEM_FAIL_MAX_STR - 1)
-		mem_fail_str[mem_fail_cur_idx * MEM_FAIL_MAX_CHAR + n] = '\n';
-	else
-		mem_fail_str[mem_fail_cur_idx * MEM_FAIL_MAX_CHAR + n] = 0;
-	mem_fail_cur_idx++;
-	if (mem_fail_cur_idx == MEM_FAIL_MAX_STR)
-		mem_fail_cur_idx = 0;
-	HA_SPIN_UNLOCK(POOL_LOCK, &mem_fail_lock);
 	return ret;
 
 }