Revert "[runtime] Decrease StringTable shrink limit"

This reverts commit 868ed8ee.

Reason for revert:
https://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20debug/builds/19753

Original change's description:
> [runtime] Decrease StringTable shrink limit
> 
> Given that we have not seen any regressions yet we're trying a more aggressive
> limit.
> 
> Bug: chromium:818642, v8:5443
> Change-Id: Ic45001ed6c042fc31cbba0d417d5060d2de8fb3a
> Reviewed-on: https://chromium-review.googlesource.com/975126
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Commit-Queue: Camillo Bruni <cbruni@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52145}

TBR=mlippautz@chromium.org,cbruni@chromium.org

Change-Id: Ic1f3ab2aa7683e5fc9118f196e5a31eb55a9a5a0
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:818642, v8:5443
Reviewed-on: https://chromium-review.googlesource.com/975741Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52148}

src/objects/string-table.h

@@ -78,7 +78,7 @@ class StringTable : public HashTable<StringTable, StringTableShape> {
 
   DECL_CAST(StringTable)
 
-  static const int kMaxEmptyFactor = 8;
+  static const int kMaxEmptyFactor = 16;
   static const int kMinCapacity = 2048;
   static const int kMinShrinkCapacity = kMinCapacity;