Revert "insights: execute database migrations (#17586)"

Created by: slimsag

This reverts #17586 / commit b8774037e7aff1d309c254ce318ede756922b0dc.

This passed in my PR branch on CI, it appears to be failing only in the server docker image - which is super odd because the code shouldn't run there at all: https://github.com/sourcegraph/sourcegraph/pull/17586/files#diff-f086a52919b26953bebd029dda555b5ae3ac420c03816d8f82592a34eed15694R17-R21

I'll debug and re-land this change tomorrow, reverting for now to fix CI.