Remove unused function `size_pool_for_size`

```
compiling ../gc.c
../gc.c:2444:1: warning: unused function 'size_pool_for_size' [-Wunused-function]
size_pool_for_size(rb_objspace_t *objspace, size_t size)
^
1 warning generated.
```

1 files changed, 0 insertions, 14 deletions

diff --git a/gc.c b/gc.c
index d3dc51f221..8db4f0f8f5 100644
--- a/gc.c
+++ b/gc.c
@@ -2443,20 +2443,6 @@ size_pool_idx_for_size(size_t size)
 #endif
 }
 
-#if USE_RVARGC
-static inline rb_size_pool_t *
-size_pool_for_size(rb_objspace_t *objspace, size_t size)
-{
-    size_t size_pool_idx = size_pool_idx_for_size(size);
-
-    rb_size_pool_t *size_pool = &size_pools[size_pool_idx];
-    GC_ASSERT(size_pool->slot_size >= (short)size);
-    GC_ASSERT(size_pool_idx == 0 || size_pools[size_pool_idx - 1].slot_size < (short)size);
-
-    return size_pool;
-}
-#endif
-
 ALWAYS_INLINE(static VALUE newobj_slowpath(VALUE klass, VALUE flags, rb_objspace_t *objspace, rb_ractor_t *cr, int wb_protected, size_t size_pool_idx));
 
 static inline VALUE