Remove assert statements in autoninja.py

These were introduced in crrev.com/c/6024739 and currently break
autoninja for non-Googlers who manually enable Siso by setting the
use_siso=true GN arg.

$ gn gen --args='use_siso=true' out/Debug
$ autoninja -C out/Debug base
Traceback (most recent call last):
  File "/home/philwo/depot_tools/autoninja.py", line 504, in <module>
    sys.exit(main(sys.argv))
                ^^^^^^^^^^^^^^
  File "/home/philwo/depot_tools/autoninja.py", line 493, in main
    exit_code = _main_inner(input_args, build_id, should_collect_logs)
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/philwo/depot_tools/autoninja.py", line 249, in _main_inner
    assert use_siso != False
           ^^^^^^^^^^^^^^^^^
AssertionError

R=ukai@google.com

Change-Id: I6536576d39b4ef094daa4e7ec80f3d743ecefd85
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6058992
Auto-Submit: Philipp Wollermann <philwo@google.com>
Reviewed-by: Fumitoshi Ukai <ukai@google.com>
Commit-Queue: Fumitoshi Ukai <ukai@google.com>

autoninja.py

@@ -246,19 +246,15 @@ def _main_inner(input_args, build_id, should_collect_logs=False):
                 use_remoteexec = False
                 continue
             if k == "use_siso" and v == "true":
-                assert use_siso != False
                 use_siso = True
                 continue
             if k == "use_siso" and v == "false":
-                assert use_siso != True
                 use_siso = False
                 continue
             if k == "use_reclient" and v == "true":
-                assert use_reclient != False
                 use_reclient = True
                 continue
             if k == "use_reclient" and v == "false":
-                assert use_reclient != True
                 use_reclient = False
                 continue
         if use_reclient is None: