Skip built? check at build time to install .rb files in exts

without additional option or manual cleanup

Author: kateinoigakukun

lib/ruby_wasm/build_system/product/crossruby.rb

@@ -186,10 +186,6 @@ def artifact
       File.join(@rubies_dir, "ruby-#{name}.tar.gz")
     end
 
-    def built?
-      File.exist?(artifact)
-    end
-
     def extinit_obj
       "#{ext_build_dir}/extinit.o"
     end

lib/ruby_wasm/rake_task.rb

@@ -68,7 +68,6 @@ def initialize(
 
     desc "Cross-build Ruby for #{@target}"
     task name do
-      next if @crossruby.built?
       @crossruby.build
     end
     namespace name do