Normalize java source file paths before running "sort -u".

We rely on "sort -u" to dedupe aidl/logtags generated java files added
by both from $(all_java_sources) and from "find
$(PRIVATE_SOURCE_INTERMEDIATES_DIR) -name '*.java".
But "sort -u" doesn't work if any of the aidl/logtags source file path
has "../" in it.
This change fixes this issue by normalizing the source file paths before
passing them to "sort -u".

Change-Id: I12d2c4e0397bed9f426a1ed9b13608d72d01e0df