get rid of test__basic_webassembly (#55)

This is an obsolete test case based on our own Chromium patch, implemented when Wasm support didn't exist yet.

In addition, it occasionally fails with the following error:

ERROR: test__basic_webassembly (tests_webassembly.test.WebassemblyTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/usertd/tests/common/utils/__init__.py", line 121, in inner_print_debug
    return method(self, *args, **kwargs)
  File "/home/usertd/tests/common/utils/__init__.py", line 98, in inner_measure_time
    return method(self, *args, **kwargs)
  File "/home/usertd/tests/common/utils/__init__.py", line 107, in inner_log_exception
    return method(self, *args, **kwargs)
  File "/home/usertd/tests/common/utils/__init__.py", line 154, in inner_average_benchmarks
    ab.run(times=int(os.environ.get('AVERAGE_BENCHMARKS_TIMES', '1')))
  File "/home/usertd/tests/common/utils/__init__.py", line 82, in run
    one_run_results = self.method(self.method_self, *self.args, **self.kwargs)
  File "/home/usertd/tests/tests_webassembly/test.py", line 36, in test__basic_webassembly
    report_win_signals = buyer_server.get_last_request("/reportWin").get_first_json_param('signals')
AttributeError: 'NoneType' object has no attribute 'get_first_json_param'

You should be using test__basic_webassembly_api instead.