Remove `pkg-config` gem dependency (#25615)

Gemfile

@@ -3,8 +3,6 @@
 source 'https://rubygems.org'
 ruby '>= 3.0.0'
 
-gem 'pkg-config', '~> 1.5'
-
 gem 'puma', '~> 6.3'
 gem 'rails', '~> 6.1.7'
 gem 'sprockets', '~> 3.7.2'

Gemfile.lock

@@ -478,7 +478,6 @@ GEM
     pg (1.5.3)
     pghero (3.3.3)
       activerecord (>= 6)
-    pkg-config (1.5.1)
     posix-spawn (0.3.15)
     premailer (1.21.0)
       addressable
@@ -833,7 +832,6 @@ DEPENDENCIES
   parslet
   pg (~> 1.5)
   pghero
-  pkg-config (~> 1.5)
   posix-spawn
   premailer-rails
   private_address_check (~> 0.5)