Bug 854478: remove support for automatically converting Sherlock-format search engines that were dropped into the profile directory, r=MattN

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extra : transplant_source : 2%EBl%CE1W%3E%A2%B3JK0%10M%0B%AF%87%C5H%AB
Bug 862143: remove support for loading sherlock files from disk, r=MattN

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extra : transplant_source : %0D%EC%3F%1E%1At%B5%23J%1F3V%F4%C8Uq%93l%F0%40
Test case for bug 880724