I planned on removing older Steam betas for some time now.
With 0.8.2 I hit Steam's maximum betas count and will have to remove at least one to be able to make a new release. So I decided to clean things up.
There currently are the following betas:
0.3.4
0.3.5
0.3.6
0.3.7
0.3.8
0.3.9
0.4.0
0.4.1
0.4.2
0.5.0
0.5.1
0.5.2
0.5.3
0.5.4
0.5.5
0.6.0
0.6.1
0.6.2
0.6.3
0.7.0
0.7.1
0.8.0
0.8.1
0.8.2

With MAJOR.MINOR.PATCH versioning, I plan on keeping the highest patch version of every minor version (plus recent ones regardless).

Which means the following will remain:
0.3.9
0.4.2
0.5.5
0.6.3
0.7.1
0.8.0
0.8.1
0.8.2

If you are playing on one of the to-be-removed ones, please pick the matching minor version, so you can continue playing with your savegame.
E.g. if you were on 0.3.3, pick 0.3.9 . If you were on 0.5.0 pick 0.5.5.
Please also let me know if you're actually using the betas, since I could remove more if there's no demand for them.
I'll wait at least a week from now until removal (unless I have to release a new version to fix a bug).