Drop deprecated -S option from erb command

We attempted to remove things like this and reverted all of them, but I
think nobody relies on this unlike the positional arguments of
`ERB#initialize`.

Author: k0kubun

NEWS.md

@@ -1,5 +1,9 @@
 # Change Log
 
+## Unreleased
+
+- Drop deprecated `-S` option from `erb` command
+
 ## 3.0.0
 
 - Bump `required_ruby_version` to Ruby 2.7+ [#23](https://github.com/ruby/erb/pull/23)

libexec/erb

@@ -74,11 +74,6 @@ class ERB
             $DEBUG = true
           when '-r'                        # require
             require ARGV.req_arg
-          when '-S'                        # security level
-            warn 'warning: -S option of erb command is deprecated. Please do not use this.'
-            arg = ARGV.req_arg
-            raise "invalid safe_level #{arg.dump}" unless arg =~ /\A[0-1]\z/
-            safe_level = arg.to_i
           when '-T'                        # trim mode
             arg = ARGV.req_arg
             if arg == '-'
@@ -127,12 +122,7 @@ EOU
       filename = $FILENAME
       exit 2 unless src
       trim = trim_mode_opt(trim_mode, disable_percent)
-      if safe_level.nil?
-        erb = factory.new(src, trim_mode: trim)
-      else
-        # [deprecated] This will be removed at Ruby 2.7.
-        erb = factory.new(src, safe_level, trim_mode: trim)
-      end
+      erb = factory.new(src, trim_mode: trim)
       erb.filename = filename
       if output
         if number

test/erb/test_erb_command.rb

@@ -17,17 +17,4 @@ def test_template_file_encoding
                        File.expand_path("../../libexec/erb", __dir__)],
                       "<%=''.encoding.to_s%>", ["UTF-8"])
   end
-
-  # These interfaces will be removed at Ruby 2.7.
-  def test_deprecated_option
-    pend if RUBY_ENGINE == 'truffleruby'
-    warnings = [
-      "warning: -S option of erb command is deprecated. Please do not use this.",
-      /\n.+\/libexec\/erb:\d+: warning: Passing safe_level with the 2nd argument of ERB\.new is deprecated\. Do not use it, and specify other arguments as keyword arguments\.\n/,
-    ]
-    assert_in_out_err(["-I#{File.expand_path('../../lib', __dir__)}",
-                       File.expand_path("../../libexec/erb", __dir__),
-                       "-S", "0"],
-                      "hoge", ["hoge"], warnings)
-  end
 end