adb: fix unicode file path test.

This test is failing due to:

     UnicodeWarning: Unicode equal comparison failed to convert both
     arguments to Unicode - interpreting them as being unequal'

Both arguments are already unicode, so stop encoding one side.

Test: python -m unittest test_device.FileOperationsTest.test_unicode_paths
Change-Id: Iea8bf29845ab3008ccf4c7dbd6969196e57ea25d