infra: Increase linux-goma-rbe-staging-rel to 100%

We have verified that the RBE-based builder is comparable in compile
time versus the class Goma builders.

Bug: 855319
Change-Id: Iacb8baea7291d82a09a839db4c72820482096af5
Reviewed-on: https://chromium-review.googlesource.com/c/1358113Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Simon Que <sque@chromium.org>
Cr-Commit-Position: refs/heads/master@{#613023}

docs/infra/cq_builders.md

@@ -261,7 +261,7 @@ as required builders.
 
   https://crbug.com/855319
 
-  * Experimental percentage: 50
+  * Experimental percentage: 100
 
 * [win7_chromium_rel_loc_exp](https://ci.chromium.org/p/chromium/builders/luci.chromium.try/win7_chromium_rel_loc_exp) ([`cq.cfg` entry](https://cs.chromium.org/search/?q=package:%5Echromium$+file:cq.cfg+win7_chromium_rel_loc_exp)) ([matching builders](https://cs.chromium.org/search/?q=file:trybots.py+win7_chromium_rel_loc_exp))
 

infra/config/branch/cq.cfg

@@ -238,7 +238,7 @@ verifiers {
       # https://crbug.com/855319
       builders {
         name: "linux-goma-rbe-staging-rel"
-        experiment_percentage: 50
+        experiment_percentage: 100
       }
       builders {
         name: "win7_chromium_rel_loc_exp"