Drop pathname from Gemfile for Ruby 4

* Pathname is builtin since Ruby 4.0
* Pathname was default gem Ruby <4.0 — we don’t need it in Gemfile

Author: soutaro

Gemfile

@@ -30,7 +30,6 @@ group :libs do
   gem "dbm"
   gem "mutex_m"
   gem "nkf"
-  gem "pathname"
 end
 
 group :profilers do

Gemfile.lock

@@ -80,7 +80,6 @@ GEM
     parser (3.3.10.0)
       ast (~> 2.4.1)
       racc
-    pathname (0.4.0)
     power_assert (3.0.1)
     prism (1.6.0)
     pstore (0.2.0)
@@ -201,7 +200,6 @@ DEPENDENCIES
   net-smtp
   nkf
   ostruct
-  pathname
   pstore
   raap
   rake

lib/rbs.rb

@@ -4,7 +4,7 @@
 
 require "set"
 require "json"
-require "pathname"
+require "pathname" unless defined?(Pathname)
 require "pp"
 require "ripper"
 require "logger"