Correct Catalyst version required

This is the version specified in dist.ini, and indeed attempting to use
5.90007 doesn't work (->env method in the wrong place).
Merge Catalyst and Catalyst::Runtime dependencies

Catalyst and Catalyst::Runtime both come from a single distribution
(Catalyst-Runtime) and share a version number, so it isn't necessary to
specify both of them -- and it's confusing to specific a different number
for each.

Put the version dependency on Catalyst::Runtime, since that's the module
that MetaCPAN::Web actually tries to load a specific version of.
Express missing prereqs to make the scanner happy

It's finally empty!