Remove redundant early return in livecheck skip_conditions

[Rylan12]

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This is currently blocking #17586, #17586, and #17587:

$ brew typecheck
livecheck/skip_conditions.rb:233: This code is unreachable https://srb.help/7006
     233 |        return {} unless checks
                  ^^^^^^^^^
    livecheck/skip_conditions.rb:233: This condition was always `truthy` (`[Symbol, Symbol, Symbol, Symbol, Symbol]`)
     233 |        return {} unless checks
                                   ^^^^^^
  Got `[Symbol, Symbol, Symbol, Symbol, Symbol] (5-tuple)` originating from:
    livecheck/skip_conditions.rb:188:
     188 |      FORMULA_CHECKS = [
                ^^^^^^^^^^^^^^
    livecheck/skip_conditions.rb:233: This condition was always `truthy` (`[Symbol, Symbol, Symbol, Symbol, Symbol, Symbol]`)
     233 |        return {} unless checks
                                   ^^^^^^
  Got `[Symbol, Symbol, Symbol, Symbol, Symbol, Symbol] (6-tuple)` originating from:
    livecheck/skip_conditions.rb:197:
     197 |      CASK_CHECKS = [
                ^^^^^^^^^^^
    livecheck/skip_conditions.rb:233: This condition was always `truthy` (`[Symbol]`)
     233 |        return {} unless checks
                                   ^^^^^^
  Got `[Symbol] (1-tuple)` originating from:
    livecheck/skip_conditions.rb:207:
     207 |      RESOURCE_CHECKS = [
                ^^^^^^^^^^^^^^^

As far as I can tell, brew typecheck is correct that check can never be falsey at this point. I believe that only Formula, Cask::Cask, and Resource implement #livecheckable?, so I don't think there's a way for package_or_resource to not match one of the three cases.

If we are worried, we can also change the next line to be checks&.each do |method_name|.

[MikeMcQuaid]

Thanks @Rylan12!