Speed up Subscriber#strip_trailing_question_mark
Speed up Subscriber#strip_trailing_question_mark

I noticed this method while profiling Feature#enabled?. Turns out we can
speed it up without hurting readability by using chomp instead of gsub.

    $ cat bench.rb
    require 'benchmark'

    Benchmark.bm do |x|
      x.report("gsub ") { 100000.times { %w[enabled enabled?].each { |str| str.to_s.gsub(/\?$/, '') } } }
      x.report("chomp") { 100000.times { %w[enabled enabled?].each { |str| str.to_s.chomp('?') } } }
    end
    $ ruby bench.rb
           user     system      total        real
    gsub   0.270000   0.010000   0.280000 (  0.273812)
    chomp  0.070000   0.000000   0.070000 (  0.071246)

I tried a lot of other variations (\z instead of $, gsub!, sub, sub!,
slice, slice!, chomp!) and this was the fastest.

I doubt this will have a big effect on Flipper's performance overall,
but there doesn't seem to be much downside here.

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