Remove hw_test from all release builds on R21.

TEST=cbuildbot_config_unittest.py
BUG=None
diff --git a/buildbot/cbuildbot_config.py b/buildbot/cbuildbot_config.py
index 720fe88..a4a4c33 100755
--- a/buildbot/cbuildbot_config.py
+++ b/buildbot/cbuildbot_config.py
@@ -872,13 +872,11 @@
 
 _release.add_config('x86-mario-release',
   boards=['x86-mario'],
-  hw_tests=['bvt'],
 )
 
 _config.add_group('x86-alex-release-group',
   _release.add_config('x86-alex-release',
     boards=['x86-alex'],
-    hw_tests=['bvt'],
   ),
   _release.add_config('x86-alex_he-release',
     boards=['x86-alex_he'],
@@ -903,7 +901,6 @@
 _config.add_group('x86-zgb-release-group',
   _release.add_config('x86-zgb-release',
     boards=['x86-zgb'],
-    hw_tests=['bvt'],
   ),
   _release.add_config('x86-zgb_he-release',
     boards=['x86-zgb_he'],
@@ -927,12 +924,10 @@
 
 _release.add_config('stumpy-release',
   boards=['stumpy'],
-  hw_tests=['bvt'],
 )
 
 _release.add_config('lumpy-release',
   boards=['lumpy'],
-  hw_tests=['bvt'],
 )
 
 _release.add_config('link-release',