Remove `host-debug` internal target.

Target `host-debug` to use `host` internal target with debugging
configuration.

Rakefile

@@ -97,15 +97,6 @@ MRuby.each_target do |target|
           install_D t.prerequisites.first, t.name
         end
         depfiles += [ install_path ]
-      elsif target == MRuby.targets['host-debug']
-        unless MRuby.targets['host'].gems.map {|g| g.bins}.include?([bin])
-          install_path = MRuby.targets['host-debug'].exefile("#{bin_path}/#{bin}")
-
-          file install_path => exec do |t|
-            install_D t.prerequisites.first, t.name
-          end
-          depfiles += [ install_path ]
-        end
       else
         depfiles += [ exec ]
       end

target/host-debug.rb

-MRuby::Build.new('host-debug') do |conf|
+MRuby::Build.new('host') do |conf|
   # load specific toolchain settings
 
   # Gets set by the VS command prompts.
@@ -19,5 +19,8 @@ MRuby::Build.new('host-debug') do |conf|
   # Generate mruby debugger command (require mruby-eval)
   conf.gem :core => "mruby-bin-debugger"
 
+  # test
+  enable_test
   # bintest
+  enable_bintest
 end