Prefer `delete` to `tr` when using it to remove characters from a string

[willcosgrove]

After doing some benchmarking, it looks like delete is about 19% faster than tr when removing characters from a string.

test_string = "this is the test string"

Benchmark.ips do |x|
  x.report("tr") do
    test_string.tr(" ", "")
  end

  x.report("delete") do
    test_string.delete(" ")
  end
end

Calculating -------------------------------------
          tr      6.367M (± 3.4%) i/s -     31.997M in   5.032180s
      delete      7.567M (± 6.0%) i/s -     38.022M in   5.053830s

Comparison:
      delete:  7566538.8 i/s
          tr:  6366671.2 i/s - 1.19x  slower

[joeldrapper]

Nice. I ran the browser tests and we're still good.