[infra] fix recipe bug

We shouldn't modify self.m.vars.extra_tokens in the docker flavor.

I noticed this when doing some debugging. It doesn't seem to be causing
any problems currently.

Change-Id: I2239787f8aec8a25a6a26418c633e68840f74e04
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/271058
Commit-Queue: Eric Boren <[email protected]>
Auto-Submit: Ben Wagner aka dogben <[email protected]>
Reviewed-by: Eric Boren <[email protected]>

Author: dogben

infra/bots/recipe_modules/flavor/docker.py

@@ -39,8 +39,7 @@ def _map_host_path_to_docker(self, path):
     return None
 
   def step(self, name, cmd, **unused_kwargs):
-    extra_tokens = self.m.vars.extra_tokens
-    extra_tokens.remove('Docker')
+    extra_tokens = [t for t in self.m.vars.extra_tokens if t != 'Docker']
     os = self.m.vars.builder_cfg.get('os', '')
     model = self.m.vars.builder_cfg.get('model', '')
     cpu_or_gpu = self.m.vars.builder_cfg.get('cpu_or_gpu', '')