Interpolated strings are no longer frozen with frozen-string-literal: true

* Remove freezestring instruction since this was the only usage for it.
* [Feature #17104]

spec/ruby/language/string_spec.rb

@@ -291,4 +291,21 @@ describe "Ruby String interpolation" do
 
     -> { "#{a} #{b}" }.should raise_error(Encoding::CompatibilityError)
   end
+
+  it "creates a non-frozen String" do
+    code = <<~'RUBY'
+    "a#{6*7}c"
+    RUBY
+    eval(code).should_not.frozen?
+  end
+
+  ruby_version_is "3.0" do
+    it "creates a non-frozen String when # frozen-string-literal: true is used" do
+      code = <<~'RUBY'
+      # frozen-string-literal: true
+      "a#{6*7}c"
+      RUBY
+      eval(code).should_not.frozen?
+    end
+  end
 end