Remove Bundler's duplicate vendored PubGrub

Bundler now loads Gem::PubGrub from RubyGems' copy, so drop the
Bundler::PubGrub tree and its vendoring entry, and regenerate the
Manifest. The pub_grub entry in tool/bundler/vendor_gems.rb stays
because the RubyGems-side vendoring still consumes it.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: 2 people

Manifest.txt

@@ -274,24 +274,6 @@ lib/bundler/vendor/net-http-persistent/lib/net/http/persistent.rb
 lib/bundler/vendor/net-http-persistent/lib/net/http/persistent/connection.rb
 lib/bundler/vendor/net-http-persistent/lib/net/http/persistent/pool.rb
 lib/bundler/vendor/net-http-persistent/lib/net/http/persistent/timed_stack_multi.rb
-lib/bundler/vendor/pub_grub/LICENSE.txt
-lib/bundler/vendor/pub_grub/lib/pub_grub.rb
-lib/bundler/vendor/pub_grub/lib/pub_grub/assignment.rb
-lib/bundler/vendor/pub_grub/lib/pub_grub/basic_package_source.rb
-lib/bundler/vendor/pub_grub/lib/pub_grub/failure_writer.rb
-lib/bundler/vendor/pub_grub/lib/pub_grub/incompatibility.rb
-lib/bundler/vendor/pub_grub/lib/pub_grub/package.rb
-lib/bundler/vendor/pub_grub/lib/pub_grub/partial_solution.rb
-lib/bundler/vendor/pub_grub/lib/pub_grub/rubygems.rb
-lib/bundler/vendor/pub_grub/lib/pub_grub/solve_failure.rb
-lib/bundler/vendor/pub_grub/lib/pub_grub/static_package_source.rb
-lib/bundler/vendor/pub_grub/lib/pub_grub/strategy.rb
-lib/bundler/vendor/pub_grub/lib/pub_grub/term.rb
-lib/bundler/vendor/pub_grub/lib/pub_grub/version.rb
-lib/bundler/vendor/pub_grub/lib/pub_grub/version_constraint.rb
-lib/bundler/vendor/pub_grub/lib/pub_grub/version_range.rb
-lib/bundler/vendor/pub_grub/lib/pub_grub/version_solver.rb
-lib/bundler/vendor/pub_grub/lib/pub_grub/version_union.rb
 lib/bundler/vendor/thor/LICENSE.md
 lib/bundler/vendor/thor/lib/thor.rb
 lib/bundler/vendor/thor/lib/thor/actions.rb