Revert "require rubygems/package where used"

This reverts commit b76630f73e.

  It fails with `make test-bundler BUNDLER_SPECS=runtime/setup_spec.rb:1204`

lib/rubygems/commands/unpack_command.rb

@@ -3,7 +3,6 @@ require 'rubygems/command'
 require 'rubygems/version_option'
 require 'rubygems/security_option'
 require 'rubygems/remote_fetcher'
-require 'rubygems/package'
 
 # forward-declare
 

lib/rubygems/source/local.rb

@@ -3,8 +3,6 @@
 # The local source finds gems in the current directory for fulfilling
 # dependencies.
 
-require 'rubygems/package'
-
 class Gem::Source::Local < Gem::Source
 
   def initialize # :nodoc:

lib/rubygems/source/specific_file.rb

@@ -3,8 +3,6 @@
 # A source representing a single .gem file.  This is used for installation of
 # local gems.
 
-require 'rubygems/package'
-
 class Gem::Source::SpecificFile < Gem::Source
 
   ##