[#7077] Cop name standardisation: Rename Unneeded* cops to Redundant

[scottmatthewman]

As mentioned in #7077, standardisation of cop names is a cleanup goal before a 1.0 release.

This PR removes the use of Unneeded in cop names, in favour of Redundant.

The affected cops are:

Previous cop name	New cop name
Lint/UnneededCopDisableDirective	Lint/RedundantCopDisableDirective
Lint/UnneededCopEnableDirective	Lint/RedundantCopEnableDirective
Lint/UnneededRequireStatement	Lint/RedundantRequireStatement
Lint/UnneededSplatExpansion	Lint/RedundantSplatExpansion
Style/UnneededCapitalW	Style/RedundantCapitalW
Style/UnneededCondition	Style/RedundantCondition
Style/UnneededInterpolation	Style/RedundantInterpolation
Style/UnneededPercentQ	Style/RedundantPercentQ
Style/UnneededSort	Style/RedundantSort

RuboCop's list of renamed cops (in lib/rubocop/config_obsoletion.rb) has been updated so that any settings within a user's config files will emit the appropriate message.

In terms of the settings with config/default.yml, I have gone with the precedent set in previous cop renaming commits (e.g., #6983) and set each renamed cop's VersionAdded value to the presumed next release, 0.76.

Within each cop, I've endeavoured to also change method names, constants, etc. from unneeded to redundant where such terms clearly directly relate to the cop names. For general descriptive comments or within documentation, where usage is more conversational, I've tended to keep the wording as-is.

[bbatsov]

Fantastic job! 🙇 This will frustrate our users a bit, but it's a big step towards 1.0.

[Drenmi]

Very nice! I have been thinking about this for a long time. 🎉