Remove unused imports in webkitpy.

third_party/WebKit/Tools/Scripts/webkitpy/tool/steps/abstractstep.py

 # Copyright (C) 2010 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 # copyright notice, this list of conditions and the following disclaimer
@@ skipping 10 matching lines @@
 # OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 # SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 # LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 import sys
 
-from webkitpy.common.system.executive import ScriptError
 from webkitpy.tool.steps.options import Options
 
 
 class AbstractStep(object):
     def __init__(self, tool, options):
         self._tool = tool
         self._options = options
 
     def _exit(self, code):
         sys.exit(code)
 
     @classmethod
     def options(cls):
         return [
             # We need this option here because cached_lookup uses it.  :(
             Options.git_commit,
         ]
 
     def run(self, state):
         raise NotImplementedError, "subclasses must implement"