Remove load and activate methods from ThemePackage

I assume these were added to speed theme loading, but now that promises
are being used it complicates overriding methods. From my tests removing
these methods and relying on Atom Package's methods added ~2 ms per 
theme.

src/theme-package.coffee

@@ -1,3 +1,4 @@
+Q = require 'q'
 AtomPackage = require './atom-package'
 Package = require './package'
 
@@ -15,16 +16,3 @@ class ThemePackage extends AtomPackage
 
   disable: ->
     atom.config.removeAtKeyPath('core.themes', @metadata.name)
-
-  load: ->
-    @measure 'loadTime', =>
-      try
-        @metadata ?= Package.loadMetadata(@path)
-      catch e
-        console.warn "Failed to load theme named '#{@name}'", e.stack ? e
-    this
-
-  activate: ->
-    @measure 'activateTime', =>
-      @loadStylesheets()
-      @activateNow()