Remove remaining unused imports in webkitpy.

third_party/WebKit/Tools/Scripts/webkitpy/style/checkers/png.py

 # Copyright (C) 2012 Balazs Ankes (bank@inf.u-szeged.hu) University of Szeged
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions
 # are met:
 # 1.  Redistributions of source code must retain the above copyright
 #     notice, this list of conditions and the following disclaimer.
 # 2.  Redistributions in binary form must reproduce the above copyright
 #     notice, this list of conditions and the following disclaimer in the
 #     documentation and/or other materials provided with the distribution.
 #
 # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 # A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 # 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.
 
-
 """Supports checking WebKit style in png files."""
 
-
 from webkitpy.common import read_checksum_from_png
 from webkitpy.common.system.systemhost import SystemHost
-from webkitpy.common.checkout.scm.detection import SCMDetector
 
 
 class PNGChecker(object):
     """Check svn:mime-type for checking style"""
 
     categories = set(['image/png'])
 
     def __init__(self, file_path, handle_style_error, host=None):
         self._file_path = file_path
         self._handle_style_error = handle_style_error
         self._host = host or SystemHost()
         self._fs = self._host.filesystem
 
     def check(self, inline=None):
         if self._fs.exists(self._file_path) and self._file_path.endswith("-expected.png"):
             with self._fs.open_binary_file_for_reading(self._file_path) as filehandle:
                 if not read_checksum_from_png.read_checksum(filehandle):
                     self._handle_style_error(
                         0, 'image/png', 5,
                         "Image lacks a checksum. Generate pngs using run-webkit-tests to ensure they have a checksum.")