Remove unnecessary build helper methods

These helpers are no longer needed since the logic of choosing
wether to link against the v8 library present in the system, or the
one provided by the libv8 gem has been relocated in the libv8 gem.

ext/v8/build.rb

@@ -1,52 +0,0 @@
-
-LIBV8_COMPATIBILITY = '~> 3.11.8'
-
-def have_rubygem_libv8?
-  require 'rubygems'
-  gem 'libv8', LIBV8_COMPATIBILITY
-  require 'libv8'
-  return true
-rescue Gem::LoadError
-  return false
-rescue LoadError
-  return false
-end
-
-def build_with_system_libv8
-  dir_config('v8')
-  find_header('v8.h') or begin
-    puts <<-EOS
-    The Ruby Racer requires libv8 #{LIBV8_COMPATIBILITY}
-    to be present on your system in order to compile
-    and link, but it could not be found.
-
-    In order to resolve this, you will either need to manually
-    install an appropriate libv8 and make sure that this
-    build process can find it. If you install it into the
-    standard system path, then it should just be picked up
-    automatically. Otherwise, you'll have to pass some extra
-    flags to the build process as a hint.
-
-    If you don't want to bother with all that, there is a
-    rubygem that will do all this for you. You can add
-    following line to your Gemfile:
-        gem 'libv8', '#{LIBV8_COMPATIBILITY}'
-
-    We hope that helps, and we apologize, but now we have
-    to push the eject button on this install.
-
-    thanks,
-    The Mgmt.
-
-    EOS
-    raise "unable to locate libv8. Please see output for details"
-  end
-  $LDFLAGS << " -lv8 "
-end
-
-def build_with_rubygem_libv8
-  require 'libv8'
-  include Libv8
-  $INCFLAGS.insert 0, "#{libv8_include_flags} "
-  $LDFLAGS.insert 0, libv8_objects.join(' ') + " "
-end