c2a: Our cargo works again, re-enable defaulting.

Bug: 234744235
Test: Run cargo2android.py without --cargo_bin
Test: Run in the sandbox without providing --cargo_bin
Change-Id: I4c3744e0e391ab7e4fb6a857483fde5c0015f0ff

scripts/cargo2android.py

@@ -1160,12 +1160,6 @@ class Runner(object):
         sys.exit('ERROR: cannot find cargo in ' + self.args.cargo_bin)
       print('INFO: using cargo in ' + self.args.cargo_bin)
       return
-    elif os.environ.get('ANDROID_BUILD_ENVIRONMENT_CONFIG', '') == 'googler':
-      sys.exit('ERROR: Not executed within the sandbox. Please see '
-               'go/cargo2android-sandbox for more information.')
-    else:
-      sys.exit('ERROR: the prebuilt cargo is not usable; please '
-               'use the --cargo_bin flag.')
     # We have only tested this on Linux.
     if platform.system() != 'Linux':
       sys.exit('ERROR: this script has only been tested on Linux with cargo.')