java: remove java 1.4 commented out code

Change-Id: I97b27b893ba516c6c29a46095f4ffc6fab838f1b
java: remove pre Java 1.5 workaround in UrlToFileMapper

Since we now require Java 1.5
Note that I tried to remove more code and use URL#toURI as the comment
suggests, but that results in errors during make check.

Change-Id: If283ee60f272b18920dcf8fc1be8766c0bed6ea5