Remove empty result_set_to_ruby_data_type method

The method was defined as an empty stub in JDBCConnection (`def ... end`
with no body, returning nil). It had zero call sites anywhere in lib/ or
spec/, no dynamic dispatch construction targets the name, and the
enclosing class is tagged `# :nodoc:` so it is not part of a documented
public API. Drop the dead code.

Net change: -3 LOC. No behavior change. Full suite is green
(468 examples, 0 failures, 1 pre-existing pending).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: yahonda

lib/plsql/jdbc_connection.rb

@@ -390,9 +390,6 @@ def get_ruby_value_from_result_set(rset, i, metadata)
       ora_value_to_ruby_value(ora_value)
     end
 
-    def result_set_to_ruby_data_type(column_type, column_type_name)
-    end
-
     def plsql_to_ruby_data_type(metadata)
       data_type, data_length = metadata[:data_type], metadata[:data_length]
       case data_type