housekeeping: Unconditionally write bitmap lookup tables

With lookup tables, Git has introduced a new extension for packfile bitmaps in v2.38.0 that allows it to defer loading bitmaps until they are really required. This can provide a small speedup for some short lived Git commands that don't really need all of the bitmaps to be loaded.

We have introduced the logic to write bitmap lookup tables in 73505638 (housekeeping: Enable writing bitmap lookup tables, 2023-01-18). The subsequent rollout of its feature flag has been eventless and did not surface any issues at all.

Remove the feature flag and unconditionally enable writing of bitmap lookup tables.

Changelog: changed

Closes #4744 (closed).