Bug#1030326: astro-python3: please stop recommending python3-theano as it is being removed

[Rebecca N. Palmer]

Package: astro-python3
Severity: minor

theano is abandoned upstream and is broken by numpy 1.24 (#1027215).  It 
is hence being removed from testing/next-stable, and probably from 
unstable as well.

Hence, please stop listing it in this metapackage.