Revert "[swarming] Dogfood exparchive feature"

This reverts commit e1f7ae33.

Reason for revert: Breaks on the bot:
https://build.chromium.org/p/client.v8/builders/V8%20Linux64%20-%20cfi/builds/8773/steps/compile/logs/stdio

Original change's description:
> [swarming] Dogfood exparchive feature
> 
> The new swarming archiving method requires isolate files to be copied to the build dir.
> 
> BUG=chromium:598990
> NOTRY=true
> TBR=tandrii@chromium.org,tansell@chromium.org,vogelheim@chromium.org
> 
> Change-Id: I87633725d9ce715684f761ce0c8d2691642c5389
> Reviewed-on: https://chromium-review.googlesource.com/444644
> Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> Commit-Queue: Michael Achenbach <machenbach@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#43266}

TBR=machenbach@chromium.org,vogelheim@chromium.org,tandrii@chromium.org,tansell@chromium.org,v8-reviews@googlegroups.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:598990

Change-Id: Ie25205f8df69981fde223a232348534487460808
Reviewed-on: https://chromium-review.googlesource.com/444225
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43271}

infra/mb/mb_config.pyl

@@ -425,7 +425,7 @@
       'gyp', 'release_bot', 'x64', 'asan', 'bb', 'coverage', 'lsan',
       'minimal_symbols', 'swarming'],
     'gyp_release_x64_cfi_symbolized': [
-      'gyp', 'release_bot', 'x64', 'cfi', 'swarming_exp', 'symbolized'],
+      'gyp', 'release_bot', 'x64', 'cfi', 'swarming', 'symbolized'],
     'gyp_release_x64_gcc_coverage': [
       'gyp', 'release_bot', 'x64', 'coverage', 'gcc'],
 
@@ -635,11 +635,6 @@
       'gyp_defines': 'test_isolation_mode=prepare',
     },
 
-    'swarming_exp': {
-      'gn_args': 'v8_test_isolation_mode="check"',
-      'gyp_defines': 'test_isolation_mode=check',
-    },
-
     # TODO(machenbach): Remove the symbolized config after the bots are gone.
     'symbolized': {
       'gn_args': 'v8_no_inline=true',