Revert "Make sure that we don't perform in-place mutation on SafeBuffer string"

This reverts commit 115e80dccc.

actionpack/lib/action_view/template.rb

@@ -218,9 +218,6 @@ module ActionView
         method_name = self.method_name
 
         if source.encoding_aware?
-          # Avoid performing in-place mutation for SafeBuffer
-          @source = source.to_str if source.html_safe?
-
           # Look for # encoding: *. If we find one, we'll encode the
           # String in that encoding, otherwise, we'll use the
           # default external encoding.

actionpack/test/template/template_test.rb

@@ -172,10 +172,5 @@ class TestERBTemplate < ActiveSupport::TestCase
     ensure
       silence_warnings { Encoding.default_external = old }
     end
-
-    def test_render_inline_safebuffer_should_not_raise_error
-      @template = new_template("Hello".html_safe)
-      render
-    end
   end
 end