Returns a copy of +self+ with trailing substring <tt>suffix</tt> removed:

  'foo'.delete_suffix('o')           # => "fo"
  'foo'.delete_suffix('oo')          # => "f"
  'foo'.delete_suffix('foo')         # => ""
  'foo'.delete_suffix('f')           # => "foo"
  'foo'.delete_suffix('x')           # => "foo"
  'тест'.delete_suffix('ст')         # => "те"
  'こんにちは'.delete_suffix('ちは')  # => "こんに"

Related: see {Converting to New String}[rdoc-ref:String@Converting+to+New+String].
