[services] Remove dependency sources from Docker image

Summary:
The dependency libraries are built and installed to system directories (eg. /usr/local/lib). The source code is not needed and just bloats the Docker image.

This change reduces the size of the tunnelbroker-server image from 5.37GB to 3.52GB.

Test Plan: npm run build-all

Reviewers: ashoat, karol-bisztyga, geekbrother

Reviewed By: ashoat, karol-bisztyga

Subscribers: palys-swm, Adrian, atul, benschac

Differential Revision: https://phabricator.ashoat.com/D3403