Revert "Simplify full-core.gembox"

This reverts commit e20d652f22.
This change cannot handle hidden dependency between `mruby-print` and
`mruby-sprintf`; ref #4202

mrbgems/full-core.gembox

@@ -1,6 +1,9 @@
 MRuby::GemBox.new do |conf|
+  conf.gem :core => "mruby-sprintf"
+  conf.gem :core => "mruby-print"
+
   Dir.glob("#{root}/mrbgems/mruby-*/mrbgem.rake") do |x|
     g = File.basename File.dirname x
-    conf.gem :core => g unless g =~ /^mruby-(?:bin-debugger|test)$/
+    conf.gem :core => g unless g =~ /^mruby-(print|sprintf|bin-debugger|test)$/
   end
 end