[zone] Fix allocate method of ZoneAllocator

This removes two unneeded casts and an unused parameter.
Note that according to the specification, {Allocator}s need to provide
an {allocate} method receiving the size {n}, and *optionally* they can
support {allocate} with a second pointer parameter which they can use
in an unspecified manner. Since we do not use the second argument, we
should just not provide that method.

Drive-by: Remove else-after-return.

R=mlippautz@chromium.org

Bug: v8:9396
Change-Id: I776c5ae2f6652e20c9f9bfd511c41ce6ad1c1329
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1690831
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62561}

src/zone/zone-allocator.h

@@ -47,11 +47,8 @@ class ZoneAllocator {
   template <typename U>
   friend class ZoneAllocator;
 
-  T* allocate(size_t n, const void* hint = nullptr) {
-    return static_cast<T*>(zone_->NewArray<T>(static_cast<int>(n)));
-  }
-  void deallocate(T* p, size_t) { /* noop for Zones */
-  }
+  T* allocate(size_t n) { return zone_->NewArray<T>(n); }
+  void deallocate(T* p, size_t) {}  // noop for zones
 
   size_t max_size() const {
     return std::numeric_limits<int>::max() / sizeof(T);
@@ -100,16 +97,15 @@ class RecyclingZoneAllocator : public ZoneAllocator<T> {
   template <typename U>
   friend class RecyclingZoneAllocator;
 
-  T* allocate(size_t n, const void* hint = nullptr) {
+  T* allocate(size_t n) {
     // Only check top block in free list, since this will be equal to or larger
     // than the other blocks in the free list.
     if (free_list_ && free_list_->size >= n) {
       T* return_val = reinterpret_cast<T*>(free_list_);
       free_list_ = free_list_->next;
       return return_val;
-    } else {
-      return ZoneAllocator<T>::allocate(n, hint);
     }
+    return ZoneAllocator<T>::allocate(n);
   }
 
   void deallocate(T* p, size_t n) {