Remove const_get from StringIdentifierArgument target

[Fix rubocop#425]
`const_get` doesn't accept symbols that are something like
`:"Foo::Bar"`, and that's intended according to this issue.
https://bugs.ruby-lang.org/issues/12319
Therefore, changing String to Symbol might not work as expected.
As far as I know that's related to `const_get` only so we can remove
it from the target of `StringIdentifierArgument`

lib/rubocop/cop/performance/string_identifier_argument.rb

@@ -38,7 +38,7 @@ class StringIdentifierArgument < Base
         # And `attr` may not be used because `Style/Attr` registers an offense.
         # https://github.com/rubocop/rubocop-performance/issues/278
         RESTRICT_ON_SEND = (%i[
-          class_variable_defined? const_defined? const_get const_set const_source_location
+          class_variable_defined? const_defined? const_set const_source_location
           define_method instance_method method_defined? private_class_method? private_method_defined?
           protected_method_defined? public_class_method public_instance_method public_method_defined?
           remove_class_variable remove_method undef_method class_variable_get class_variable_set