Move the source DB builder into pyls since pyre does not need it anymore

Summary: Original discussion on this diff - D31055253 (71c05f3). grievejia mentioned that the Pyre team doesn't need this dep anymore, so let's just shovel it into PYLS so we can mess with it to our heart's content.

Reviewed By: grievejia

Differential Revision: D31406584

fbshipit-source-id: 6e4b2a1bc937c3aa253f5005141b6f23d7d324ff