Revert "heap: Implement DiscardSystemPages for Fuchsia"

This reverts commit e5d568f4.

Reason for revert: Compile error: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Fuchsia%20-%20builder/9825/overview

Original change's description:
> heap: Implement DiscardSystemPages for Fuchsia
>
> Bug: v8:12050
> Change-Id: I9fa5c0d38f277e363befbdaecaaedd4ee55bfb07
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3071208
> Reviewed-by: Wez <wez@chromium.org>
> Commit-Queue: Omer Katz <omerkatz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#76160}

Bug: v8:12050
Change-Id: I2abdadc4b47656074aa49323f9896695ab5642df
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3080576
Auto-Submit: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#76161}

src/base/platform/platform-fuchsia.cc

@@ -127,10 +127,7 @@ bool OS::SetPermissions(void* address, size_t size, MemoryPermission access) {
 
 // static
 bool OS::DiscardSystemPages(void* address, size_t size) {
-  uint64_t address_int = reinterpret_cast<uint64_t>(address);
-  zx_status_t status = zx::vmar::root_self()->op_range(
-      ZX_VMO_OP_DECOMMIT, address_int, size, nullptr, 0);
-  DCHECK_EQ(ZX_OK, status);
+  // TODO(hpayer): Does Fuchsia have madvise?
   return true;
 }