Revert "Enhance hashutils with more git sha1 computations"

And its friends:

• 211b40f Revert "Add missing test use case"
• 43096fa Revert "Only sha1, sha256, sha1_git as default algorithms"
• 9fcc5d7 Revert "Enhance hashutils with more git sha1 computations"

Context:
This code is not needed in swh-core
This will be done in swh-loader-dir.