stop using deprecated properties from a4

[fuzzylogic2000]

removed propertes here: https://github.com/liqd/adhocracy4/pull/1288

still used but already removed from a4:

• [x] projects.days_left

still used, but deprecated:

• [ ] projects.active_phase

check:

• [x] templatetag get_class - was removed from a4, but is also in opin, which one are we using?

[fuzzylogic2000]

The days_left and the templatetag were fixed in #2592