misc: Rename jami-qt to jami and remove launcher script.

Now that there is no longer a second official client (jami-gnome), we
can remove this uninteresting implementation detail from the name.

Mostly automated via:

  $ git grep jami-qt -l | xargs sed 's/jami-qt/jami/g' -i

* src/app/jami: Delete launcher script.
* CMakeLists.txt: Un-register it from installation.

Change-Id: I5167c29089feb4e64c12d7d01c1ce281e16c0613