javadoc/droidoc: Don't add .jar files to sourcepath.

javadoc expects directories on the sourcepath, not jar files.
The original commit 88b60799
in 2009 was already passing the jar files, and every revision
since then seems to have kept this habit through cargo cult.

This CL removes the superfluous jar file arguments from the
sourcepath argument to javadoc.

Test: Treehugger
Bug: 76436487

Change-Id: I44b4b8ba248ad4deafbb6462e6f7398f15bd2845