Bug 1461795 - Use FileAvoidWrite when writing mozinfo.json; r=chmanchester

Since MozbuildObject.from_environment() reads from mozinfo.json, tup
picks up that file as a dependency for anything that imports buildconfig
(eg: all generated files). Using FileAvoidWrite when creating
mozinfo.json will help avoid unnecessary work after re-running configure
in the tup backend.

MozReview-Commit-ID: EEOPQYJA1MV

configure.py

@@ -108,7 +108,6 @@ def config_status(config):
     # executable permissions.
     os.chmod('config.status', 0o755)
     if config.get('MOZ_BUILD_APP') != 'js' or config.get('JS_STANDALONE'):
-        os.environ[b'WRITE_MOZINFO'] = b'1'
         from mozbuild.config_status import config_status
 
         # Some values in sanitized_config also have more complex types, such as