Remove separate JNLP substitution

With the FPI server providing redirects at a static URL in the JNLP
separate updates are no longer useful.
Revert "Update build environment to require Java 7"

This reverts commit 89beffcce8af356f8583a962b0947c553d30efe1.

nextgens warns that though retargeting to earlier Java versions is
supposed to work it might not actually do so, and in the past has not.