[rubygems/rubygems] Remove `travis_removal_info`

`travis_removal_info` is added by https://github.com/rubygems/rubygems/pull/6150. According to the comment, it's supposed to be removed at bundler v2.5.0 but it hasn't.

https://github.com/rubygems/rubygems/commit/e18797d43f

lib/bundler/cli/gem.rb

@@ -32,7 +32,6 @@ module Bundler
 
       validate_ext_name if @extension
       validate_rust_builder_rubygems_version if @extension == "rust"
-      travis_removal_info
     end
 
     def run
@@ -448,19 +447,6 @@ module Bundler
       "1.3"
     end
 
-    # TODO: remove at next minor release
-    def travis_removal_info
-      if options[:ci] == "travis"
-        Bundler.ui.error "Support for Travis CI was removed from gem skeleton generator."
-        exit 1
-      end
-
-      if Bundler.settings["gem.ci"] == "travis"
-        Bundler.ui.error "Support for Travis CI was removed from gem skeleton generator, but it is present in bundle config. Please configure another provider using `bundle config set gem.ci SERVICE` (where SERVICE is one of github/gitlab/circle) or unset configuration using `bundle config unset gem.ci`."
-        exit 1
-      end
-    end
-
     def validate_rust_builder_rubygems_version
       if Gem::Version.new(rust_builder_required_rubygems_version) > Gem.rubygems_version
         Bundler.ui.error "Your RubyGems version (#{Gem.rubygems_version}) is too old to build Rust extension. Please update your RubyGems using `gem update --system` or any other way and try again."

spec/bundler/commands/newgem_spec.rb

@@ -932,24 +932,6 @@ RSpec.describe "bundle gem" do
       end
     end
 
-    context "--ci set to travis" do
-      it "generates a GitHub Actions config file" do
-        bundle "gem #{gem_name} --ci=travis", raise_on_error: false
-        expect(err).to include("Support for Travis CI was removed from gem skeleton generator.")
-
-        expect(bundled_app("#{gem_name}/.travis.yml")).to_not exist
-      end
-    end
-
-    context "--ci set to travis" do
-      it "generates a GitHub Actions config file" do
-        bundle "gem #{gem_name} --ci=travis", raise_on_error: false
-        expect(err).to include("Support for Travis CI was removed from gem skeleton generator.")
-
-        expect(bundled_app("#{gem_name}/.travis.yml")).to_not exist
-      end
-    end
-
     context "--ci set to github" do
       it "generates a GitHub Actions config file" do
         bundle "gem #{gem_name} --ci=github"
@@ -1000,18 +982,6 @@ RSpec.describe "bundle gem" do
       end
     end
 
-    context "gem.ci setting set to travis" do
-      it "errors with friendly message" do
-        bundle "config set gem.ci travis"
-        bundle "gem #{gem_name}", raise_on_error: false
-
-        expect(err).to include("Support for Travis CI was removed from gem skeleton generator,")
-        expect(err).to include("bundle config unset gem.ci")
-
-        expect(bundled_app("#{gem_name}/.travis.yml")).to_not exist
-      end
-    end
-
     context "gem.ci setting set to github" do
       it "generates a GitHub Actions config file" do
         bundle "config set gem.ci github"

test/rubygems/test_gem_commands_setup_command.rb

@@ -31,7 +31,6 @@ class TestGemCommandsSetupCommand < Gem::TestCase
       bundler/lib/bundler/man/gemfile.5
       bundler/lib/bundler/man/gemfile.5.ronn
       bundler/lib/bundler/templates/.circleci/config.yml
-      bundler/lib/bundler/templates/.travis.yml
     ]
 
     create_dummy_files(filelist)
@@ -178,7 +177,6 @@ class TestGemCommandsSetupCommand < Gem::TestCase
       assert_path_exist File.join(dir, "bundler/b.rb")
 
       assert_path_exist File.join(dir, "bundler/templates/.circleci/config.yml")
-      assert_path_exist File.join(dir, "bundler/templates/.travis.yml")
     end
   end