[infra] Remove use_rbe from mb config

use_rbe has been deprecated and logic formerly checking it now checks for use_remoteexec first

Bug: chromium:1247781
Change-Id: I665e76345d5c1a64c2f5253799cee818a4b39129
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3707092Reviewed-by: Liviu Rau <liviurau@chromium.org>
Commit-Queue: Richard Wang <richardwa@google.com>
Cr-Commit-Position: refs/heads/main@{#81243}

infra/mb/mb_config.pyl

@@ -818,7 +818,7 @@
     },
 
     'reclient': {
-      'gn_args': 'use_rbe=true use_remoteexec=true',
+      'gn_args': 'use_remoteexec=true',
     },
 
     'release': {