Remove deprecated `String#encoding_aware?`

core extensions (`core_ext/string/encoding`).

activesupport/CHANGELOG.md

+*   Remove deprecated `String#encoding_aware?` core extensions (`core_ext/string/encoding`).
+
+    *Arun Agrawal*
+
 *   Remove deprecated `Module#local_constant_names` in favor of `Module#local_constants`.
 
     *Arun Agrawal*

activesupport/lib/active_support/core_ext/string/encoding.rb

-require 'active_support/deprecation'
-
-class String
-  def encoding_aware?
-    ActiveSupport::Deprecation.warn 'String#encoding_aware? is deprecated'
-    true
-  end
-end

activesupport/test/abstract_unit.rb

@@ -8,7 +8,6 @@
 end
 
 require 'active_support/core_ext/kernel/reporting'
-require 'active_support/core_ext/string/encoding'
 
 silence_warnings do
   Encoding.default_internal = "UTF-8"

activesupport/test/core_ext/string_ext_test.rb

@@ -651,12 +651,6 @@ def to_s
     assert_equal 'foo'.to_yaml, 'foo'.html_safe.to_yaml(:foo => 1)
   end
 
-  test 'knows whether it is encoding aware' do
-    assert_deprecated do
-      assert 'ruby'.encoding_aware?
-    end
-  end
-
   test "call to_param returns a normal string" do
     string = @string.html_safe
     assert string.html_safe?