Revert "luci: increase the experimental percentage to 100 from 70 for MM-x86-rel"

This reverts commit bce662eb.

Reason for revert: Getting pending alerts for builders that use the
16-core SSD machines.

Original change's description:
> luci: increase the experimental percentage to 100 from 70 for MM-x86-rel
>
> The pool has plenty of 4-cores for extra builds: http://shortn/_koR1dg8Vvu
> Also the host pool also has plenty of rooms: http://shortn/_xqhW5Z67ft
>
> Bug: 997376, 1127110
> Change-Id: I56b432d960c2f1821934667ac2f38d3fcb4705bf
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2450331
> Reviewed-by: Ben Pastene <bpastene@chromium.org>
> Commit-Queue: Haiyang Pan <hypan@google.com>
> Cr-Commit-Position: refs/heads/master@{#813888}

TBR=liaoyuke@chromium.org,bpastene@chromium.org,hypan@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 997376
Bug: 1127110
Change-Id: Ie3265e71b0604ea6d40a1612b820acffb8c79b8e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2530204Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
Commit-Queue: Garrett Beaty <gbeaty@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825946}

infra/config/generated/commit-queue.cfg

@@ -247,7 +247,7 @@ config_groups {
       }
       builders {
         name: "chromium/try/android-marshmallow-x86-rel"
-        experiment_percentage: 100
+        experiment_percentage: 70
         location_regexp: ".*"
         location_regexp_exclude: ".+/[+]/docs/.+"
         location_regexp_exclude: ".+/[+]/infra/config/.+"

infra/config/generated/cq-builders.md

@@ -345,7 +345,7 @@ by CQ. These are often used to test new configurations before they are added
 as required builders.
 
 * [android-marshmallow-x86-rel](https://ci.chromium.org/p/chromium/builders/try/android-marshmallow-x86-rel) ([definition](https://cs.chromium.org/search?q=package:%5Echromium$+file:/cq.star$+-file:/beta/+-file:/stable/+android-marshmallow-x86-rel)) ([matching builders](https://cs.chromium.org/search?q=+file:trybots.py+android-marshmallow-x86-rel))
-  * Experiment percentage: 100
+  * Experiment percentage: 70
 
 * [fuchsia-compile-x64-dbg](https://ci.chromium.org/p/chromium/builders/try/fuchsia-compile-x64-dbg) ([definition](https://cs.chromium.org/search?q=package:%5Echromium$+file:/cq.star$+-file:/beta/+-file:/stable/+fuchsia-compile-x64-dbg)) ([matching builders](https://cs.chromium.org/search?q=+file:trybots.py+fuchsia-compile-x64-dbg))
   * Experiment percentage: 50

infra/config/subprojects/chromium/try.star

@@ -345,7 +345,7 @@ try_.chromium_android_builder(
     goma_jobs = goma.jobs.J300,
     ssd = True,
     tryjob = try_.job(
-        experiment_percentage = 100,
+        experiment_percentage = 70,
     ),
 )