Remove local ffi-clang path from Gemfile

Monkey patches cover all needed fixes from unreleased ffi-clang,
so the published gem works everywhere.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: cfis

Gemfile

@@ -1,11 +1,3 @@
 source 'https://rubygems.org'
 
 gemspec
-
-unless ENV['CI']
-  if RUBY_PLATFORM =~ /linux/ && File.exist?('/mnt/c')
-    gem "ffi-clang", path: "/mnt/c/Source/ffi-clang"  # WSL
-  else
-    gem "ffi-clang", path: "c:/Source/ffi-clang"      # Windows
-  end
-end