[cr] Do not override is_component_build flag

At the moment cr tool sets is_component_build=true by default,
overriding the existing value of the flag, which is not particularly
helpful when trying to use is_official_build=true.

This patch disables this functionality and removes all smartness
associated with trying to guess the correct is_component_build,
leaving the user free to choose whatever they please.

R=skyostil@chromium.org

Change-Id: I8953e0e3e8fea676b044d04460b418f310b9656c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1807829Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Commit-Queue: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697177}

tools/cr/cr/actions/gn.py

@@ -14,10 +14,6 @@ GN_ARG_PREFIX = 'GN_ARG_'
 class GnPrepareOut(cr.PrepareOut):
   """A prepare action that runs gn whenever you select an output directory."""
 
-  ACTIVE = cr.Config.From(
-      GN_ARG_is_component_build='true',
-  )
-
   @property
   def priority(self):
     return -1