Revert "[heap] Enable large objects in young generation"

This reverts commit 932a5ca8.

Reason for revert: breaks GC stress

Original change's description:
> [heap] Enable large objects in young generation
> 
> Bug: chromium:852420
> Change-Id: Id1cde3450c5ca046029b17eee5dbe5132f299c3d
> Reviewed-on: https://chromium-review.googlesource.com/c/1477212
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#59669}

TBR=ulan@chromium.org,hpayer@chromium.org,mlippautz@chromium.org

Change-Id: I16f0705cf37fdc1708c605abd76d79dac3f1e825
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:852420
Reviewed-on: https://chromium-review.googlesource.com/c/1477278Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59672}

src/flag-definitions.h

@@ -818,7 +818,7 @@ DEFINE_BOOL(fast_promotion_new_space, false,
 
 DEFINE_BOOL(clear_free_memory, false, "initialize free memory with 0")
 
-DEFINE_BOOL(young_generation_large_objects, true,
+DEFINE_BOOL(young_generation_large_objects, false,
             "allocates large objects by default in the young generation large "
             "object space")