Revert "Fix building with 1.8 BASERUBY"

This reverts commit 05bc14d81a.

We have decided that the cost of reintroducing support for 1.8
BASERUBY outweighs the benefit.  If you are still using 1.8 and want
to build master/trunk, build and install the latest release, and use
that as BASERUBY.

common.mk

@@ -785,9 +785,9 @@ extconf: $(PREP)
 
 $(RBCONFIG): $(srcdir)/tool/mkconfig.rb config.status $(srcdir)/version.h
 	$(Q)$(BOOTSTRAPRUBY) -n \
-	-e 'BEGIN{VERSION=ARGV.shift;MIS=ARGV.dup}' \
-	-e 'END{abort "UNICODE version mismatch: #{MIS}" unless MIS.empty?}' \
-	-e '(MIS.delete(ARGF.path); ARGF.close) if /ONIG_UNICODE_VERSION_STRING +"#{Regexp.quote(VERSION)}"/o' \
+	-e 'BEGIN{version=ARGV.shift;mis=ARGV.dup}' \
+	-e 'END{abort "UNICODE version mismatch: #{mis}" unless mis.empty?}' \
+	-e '(mis.delete(ARGF.path); ARGF.close) if /ONIG_UNICODE_VERSION_STRING +"#{Regexp.quote(version)}"/o' \
 	$(UNICODE_VERSION) $(UNICODE_DATA_HEADERS)
 	$(Q)$(BOOTSTRAPRUBY) $(srcdir)/tool/mkconfig.rb \
 		-arch=$(arch) -version=$(RUBY_PROGRAM_VERSION) \

tool/colorize.rb

@@ -4,7 +4,7 @@ class Colorize
   def initialize(color = nil)
     @colors = @reset = nil
     if color or (color == nil && STDOUT.tty?)
-      if (/\A\e\[.*m\z/ =~ IO.popen("tput smso", "r", :err => IO::NULL, &:read) rescue nil)
+      if (/\A\e\[.*m\z/ =~ IO.popen("tput smso", "r", err: IO::NULL, &:read) rescue nil)
         @beg = "\e["
         @colors = (colors = ENV['TEST_COLORS']) ? Hash[colors.scan(/(\w+)=([^:\n]*)/)] : {}
         @reset = "#{@beg}m"

tool/downloader.rb

@@ -173,7 +173,7 @@ class Downloader
       if cache_save
         save_cache(cache, file, name)
       end
-      return file.respond_to?(:to_path) ? file.to_path : file.to_s
+      return file.to_path
     end
     if dryrun
       puts "Download #{url} into #{file}"

tool/generic_erb.rb

@@ -33,9 +33,8 @@ unchanged = color.pass("unchanged")
 updated = color.fail("updated")
 
 result = templates.map do |template|
-  method = ERB.instance_method(:initialize)
-  if method.respond_to?(:parameters) && method.parameters.assoc(:key) # Ruby 2.6+
-    erb = ERB.new(File.read(template), :trim_mode => '%-')
+  if ERB.instance_method(:initialize).parameters.assoc(:key) # Ruby 2.6+
+    erb = ERB.new(File.read(template), trim_mode: '%-')
   else
     erb = ERB.new(File.read(template), nil, '%-')
   end