Simplify requirements.yml

[joshmoore]

[WARNING]: - dependency ome.omero_common (None) from role ome.omero_web differs
from already installed version (0.3.2), skipping
- adding dependency: ome.omego
[WARNING]: - dependency ome.basedeps (None) from role ome.omero_web differs
from already installed version (1.1.0), skipping
[WARNING]: - dependency ome.ice (None) from role ome.omero_web differs from
already installed version (3.1.0), skipping
- adding dependency: ome.nginx