[PATCH 1/4] requirements: Remove psycopg2

[Finucane, Stephen]

> It would be good to provide the required packages for devs using both
> MySQL and PostgreSQL. However, there does not appear to be any way to
> specify an exclusive-or condition in pip requirements files and the
> existing behavior of including dependencies for both RDBMSs means
> system packages have to be installed for both, when you are likely
> only using one. This is particularly problematic when you want to
> set up a fast dev environment using something like Vagrant.
> 
> Settle on MySQL for now, until such a time as the consensus is to go
> all-in with PostgreSQL (including docs, for example).
> 
> Signed-off-by: Stephen Finucane <stephen.finucane at intel.com>

Merged.