Also remove selenium-webdriver from example app

It conflicts with the one from `Gemfile-rails-dependencies`

```
[!] There was an error parsing `Gemfile`:
[!] There was an error parsing `Gemfile-rails-dependencies`: You cannot specify the same gem twice with different version requirements.
You specified: selenium-webdriver (>= 4.0.0.rc1) and selenium-webdriver (>= 0). Bundler cannot continue.

 #  from /Users/pirj/source/rspec-dev/repos/rspec-rails/Gemfile-rails-dependencies:13
 #  -------------------------------------------
 #    gem 'activerecord-jdbcsqlite3-adapter', git: 'https://github.com/jruby/activerecord-jdbc-adapter', platforms: [:jruby]
 >    gem 'selenium-webdriver', require: false
 #  when /stable$/
 #  -------------------------------------------
. Bundler cannot continue.

 #  from /Users/pirj/source/rspec-dev/repos/rspec-rails/tmp/example_app/Gemfile:63
 #  -------------------------------------------
 #  eval_gemfile '/Users/pirj/source/rspec-dev/repos/rspec-rails/Gemfile-rspec-dependencies'
 >  eval_gemfile '/Users/pirj/source/rspec-dev/repos/rspec-rails/Gemfile-rails-dependencies'
 #  -------------------------------------------
```

Author: pirj

example_app_generator/generate_app.rb

@@ -19,6 +19,7 @@
   # Remove the existing rails version so we can properly use main or other
   # edge branches
   gsub_file 'Gemfile', /^.*\bgem ['"]rails.*$/, ''
+  gsub_file 'Gemfile', /^.*\bgem ['"]selenium\-webdriver.*$/, ''
   gsub_file "Gemfile", /.*web-console.*/, ''
   gsub_file "Gemfile", /.*debug.*/, ''
   gsub_file "Gemfile", /.*puma.*/, ''