- remove all places we check the flag so it's a no-op now
- flip the messaging to refer to `HOMEBREW_NO_INSTALL_FROM_API` where
relevant
- adjust the documentation
This allows HOMEBREW_INSTALL_FROM_API functionality to be disabled and will stick around once
HOMEBREW_INSTALL_FROM_API is made the default behaviour.
Co-authored-by: Eric Knibbe <enk3@outlook.com>
A new version of `shellcheck` (I think?) brought us so new warnings and
errors.
To fix:
- pass `--source-path` so we don't need to stop `shellcheck` trying to
read sourced files every time
- disable some more warnings/errors we don't care about fixing
