Comment out FPF repo setup in deb builder script

I did this for two reasons:

1. We aren't using any packages from the repo to build the debs at the
moment (if you think about it, that's kind of a catch-22), so commenting
this has no impact on building debs. Also, running `apt-get update`,
which is relativley slow, for no reason is a waste of time.

2. During testing, this created a catch-22 where I wanted to build the
debs so I could add them to the repo and publish the snapshot, but this
deb builder script wouldn't run unless the repo already existed.

We may be able to remove this code entirely, but I decided to leave it
in for now in case it is useful for something that I didn't recognize.
securedrop-grsec metapackage version should match grsec version

Previously the `Version:` of the securedrop-grsec kernel metapackage was
tracking the SecureDrop/securedrop-app-code version. Since the
metapackage tracks the grsecurity upgrades, and is independent of the
version of SecureDrop, it makes sense for the version of the metapackage
to match the grsecurity version.

Updated the deb builder (which we currently only use to build
securedrop-grsec) to get the version for the filename from the Debian
control file. This is important, since in my testing aptly refused to
add two packages with the same filename to the same repo (even if their
`Version:`s were different).

Also makes `build_meta` slightly more generic, to fit its name and
intended purpose. Also changed some variable names for clarity.
Merge branch 'develop' into release-testing

Conflicts:
	build_deb_packages.sh

The conflict was due to changing the url of the apt repository from
".pressfreedomfoundation.org" to ".freedom.press". I decided to remove
the chunk entirely (was previously commented out) since it was not used
and I cannot think of how it would ever be used.
Merge pull request #755 from freedomofpress/release-testing

securedrop-grsec build scripts