Remove unused rspec_junit_formatter dependency

This was added for Jenkins CI reporting in the 0.6.0 release (2016)
but was never wired up in Travis CI or GitHub Actions workflows.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: yahonda

ruby-plsql.gemspec

@@ -21,7 +21,6 @@ Gem::Specification.new do |s|
 
   s.add_development_dependency "rake", ">= 10.0"
   s.add_development_dependency "rspec", "~> 3.1"
-  s.add_development_dependency "rspec_junit_formatter"
   s.add_development_dependency "simplecov"
   s.add_development_dependency "ruby-oci8", "~> 2.1"
 end