Stop reading the generated ojluni sources in droiddoc.

These sources contain the result of applying the annotations from
ojluni.jaif to the ojluni sources. Now that ojluni.jaif is empty, this
is a noop, so this change switches back to reading the original
sources.

Bug: 111639530
Test: `make docs` is not affected
Change-Id: Idb98aa4f054a11bfcbcb8a84dd6f357a0a025c49