Bug 897559 - Use |repo manifest| to parse manifest

This is easier to maintain and parses some elements that were being
ignored like "remove-project".

Also no longer accept a manifest file parameter. Always use the root
workspace's current manifest.

Change-Id: Iec3a5f49c82a795dd6a6109a17d3cfcf17a98526
Revert "Bug 890065 - Add a flag for optionally disabling sources.xml"

This reverts commit 36900c6306ac6950191ddc7cb5d5b813d3649d11.

Change-Id: Ic33f60c9c5fb188a3181f2c7457e75e85980c56a