Rename flake8-builtins options to remove the "builtins" prefix

[dhruvmanila]

The "builtins" prefix for the flake8-builtins options is redundant and is inconsistent with other options like allowed-unused-imports or allowed-markup-calls.

• Rename builtins-allowed-modules -> allowed-modules
• Rename builtins-ignorelist to ignorelist

Although we can tackle this in 0.9 release, I'd say we do the rename (maintaining backwards compatibility) after the 0.9 release and hard deprecate in 0.11.

[MichaReiser]

Backward compat seems nice. We could change builtins-allowed-modules because the only rule using it is still in preview but it probably makes little sense to only add the backwards compatibility for one setting and not the other.

[MichaReiser]

Considering that both settings have the builtins prefix I don't see this blocking the release (because we renamed A005)

[AlexWaygood]

Yeah, the backwards incompatibility issue was why I didn't rename the setting at the same time as the rule (but I also didn't think hard about it; thanks @dhruvmanila for bringing this up!).

I agree that we should probably change the name of all settings together (the builtins- prefix is redundant), and going through a deprecation period. Let's add the new names for the settings (and add a deprecation message for the old ones) in the next patch release after v0.9. We can then add a hard error on using the old names for the settings from v0.11.0.