[test] Remove old Rubygems code not needed with integrated bundler

(cherry picked from commit 53a6629)

Author: chadlwilson

src/spec/ruby/spec_helper.rb

@@ -76,27 +76,9 @@ def raise_logger(level = 'WARN')
   end
 
   def gem_install_unless_installed(name, version)
-    found = nil
-    begin
-      if Gem::Specification.respond_to? :find_all
-        all = Gem::Specification.find_all
-        found = all.find do |spec|
-          spec.name == name && spec.version.to_s == version
-        end
-      elsif Gem::Specification.respond_to? :find_by_name
-        found = Gem::Specification.find_by_name name, version
-      else
-        raise Gem::LoadError unless Gem.available? name, version
-      end
-    rescue Gem::LoadError
-      found = false
-    end
-    # NOTE: won't ever be found in RubyGems >= 2.3 likely due Bundler
-    unless found
-      require 'rubygems/dependency_installer'
-      installer = Gem::DependencyInstaller.new
-      installer.install name, version
-    end
+    require 'rubygems/dependency_installer'
+    installer = Gem::DependencyInstaller.new
+    installer.install name, version
   end
 
   ExpectationNotMetError = RSpec::Expectations::ExpectationNotMetError