Revert "[compiler] Temporarily change ContextRef back to kSerialized"

This reverts commit 445f0f74.

Reason for revert: TryMakeRef is again ready for this.

Original change's description:
> [compiler] Temporarily change ContextRef back to kSerialized
>
> This can be reverted once TryMakeRef checks the heap predicate.
> I'm not reverting the previous CL because newer changes already depend
> on it.
>
> Tbr: jgruber@chromium.org
> Bug: v8:11765, v8:7790
> Change-Id: Iacc6a78a70fe6f40c9421258889c2175fb400b04
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2891579
> Reviewed-by: Georg Neis <neis@chromium.org>
> Commit-Queue: Georg Neis <neis@chromium.org>
> Auto-Submit: Georg Neis <neis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#74531}

Bug: v8:11765
Bug: v8:7790
Change-Id: I0b38791255182f1f8d0a5cf79f18d86568172487
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2897101
Commit-Queue: Georg Neis <neis@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Georg Neis <neis@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74591}

src/compiler/heap-refs.h

@@ -111,7 +111,7 @@ enum class RefSerializationKind {
   V(CallHandlerInfo, RefSerializationKind::kNeverSerialized)              \
   V(Cell, RefSerializationKind::kNeverSerialized)                         \
   V(Code, RefSerializationKind::kNeverSerialized)                         \
-  V(Context, RefSerializationKind::kSerialized)                           \
+  V(Context, RefSerializationKind::kNeverSerialized)                      \
   V(DescriptorArray, RefSerializationKind::kNeverSerialized)              \
   V(FeedbackCell, RefSerializationKind::kNeverSerialized)                 \
   V(FeedbackVector, RefSerializationKind::kNeverSerialized)               \