Remove unused coalesced variable in selective_coalesce()

The coalesced variable in selective_coalesce() was declared but never
used. Remove it to clean up the code and reduce unnecessary clutter.

Author: visitorckw

lib/malloc.c

@@ -109,15 +109,13 @@ void free(void *ptr)
 static void selective_coalesce(void)
 {
     memblock_t *p = first_free;
-    uint32_t coalesced = 0;
 
     while (p && p->next) {
         /* Merge only when blocks are FREE *and* adjacent in memory */
         uint8_t *pend = (uint8_t *) p + sizeof(memblock_t) + GET_SIZE(p);
         if (!IS_USED(p) && !IS_USED(p->next) && pend == (uint8_t *) p->next) {
             p->size = GET_SIZE(p) + sizeof(memblock_t) + GET_SIZE(p->next);
             p->next = p->next->next;
-            coalesced++;
             free_blocks_count--;
         } else {
             p = p->next;