Remove rb-readline to suppress a bunch of warnings

Something like this:
```
/home/runner/work/activerecord-import/activerecord-import/vendor/bundle/ruby/3.0.0/gems/rb-readline-0.5.5/lib/rbreadline.rb:3477: warning: assigned but unused variable - i
/home/runner/work/activerecord-import/activerecord-import/vendor/bundle/ruby/3.0.0/gems/rb-readline-0.5.5/lib/rbreadline.rb:5412: warning: parentheses after method name is interpreted as an argument list, not a decomposed argument
```

Gemfile

@@ -48,7 +48,6 @@ end
 platforms :ruby do
   gem "pry-byebug"
   gem "pry", "~> 0.12.0"
-  gem "rb-readline"
 end
 
 if version >= 4.0