completely remove `build` in favor of `python-build`

[beckermr]

Per the core call we will do the following:

• make sure the linter hints on use of build (already done, but added detail conda-forge/conda-forge-pinning-feedstock#6313)
• mark all existing build packages as broken (conda-forge/admin-requests#1049)
• make an announcement that we are doing the above (#2270)
• turn off the replacement migrator in the bot (regro/cf-scripts#2943)

cc @conda-forge/core

[jakirkham]

Thank you Matt! 🙏

[jakirkham]

Should we close out these too?

• conda-forge/python-build-feedstock#15
• conda-forge/python-build-feedstock#28

[beckermr]

Yes.