Revert "[test] Bump shards after test262 roll"

This reverts commit 1dbcc78e.

Reason for revert: Timeout has different reason. Test driver hangs.

Original change's description:
> [test] Bump shards after test262 roll
> 
> TBR=sergiyb@chromium.org
> NOTRY=true
> 
> Bug: v8:7834
> Change-Id: Ibd4e57034d493a5cc1a28049e0db0e4bb9c8f996
> Reviewed-on: https://chromium-review.googlesource.com/c/1270576
> Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> Commit-Queue: Michael Achenbach <machenbach@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#56462}

TBR=machenbach@chromium.org,sergiyb@chromium.org

Change-Id: Ic81edff220ee375f21ecd3f2ac1c2e0eeaf53878
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7834
Reviewed-on: https://chromium-review.googlesource.com/c/1270577Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56464}

infra/testing/builders.pyl

@@ -42,7 +42,7 @@
       {'name': 'benchmarks', 'variant': 'default'},
       {'name': 'v8testing', 'variant': 'default', 'shards': 4},
       {'name': 'mozilla', 'variant': 'default'},
-      {'name': 'test262_variants', 'variant': 'default', 'shards': 8},
+      {'name': 'test262_variants', 'variant': 'default', 'shards': 6},
     ],
   },
   ##############################################################################