Build: Remove manifest task

This task hasn't been used since 1.11.0 was released.

grunt.js

@@ -31,35 +31,6 @@ grunt.registerTask( "clean", function() {
 	rimraf.sync( "dist" );
 });
 
-grunt.registerTask( "manifest", "Generate categories.json manifest file", function() {
-	var categories,
-		categoryPosts = {},
-		done = this.async();
-
-	categories = require( "./" + grunt.config( "wordpress.dir" ) + "/taxonomies" ).category;
-	categories.forEach(function( category ) {
-		category.posts = categoryPosts[ category.slug ] = [];
-	});
-
-	grunt.helper( "wordpress-walk-posts", grunt.config( "wordpress.dir" ), function( post, callback ) {
-		if ( post.termSlugs && post.termSlugs.category ) {
-			post.termSlugs.category.forEach(function( slug ) {
-				categoryPosts[ slug ].push( post );
-			});
-		}
-		callback();
-	}, function( error ) {
-		if ( error ) {
-			grunt.error.log( error.message );
-			return done( false );
-		}
-
-		grunt.file.write( grunt.config( "wordpress.dir" ) + "/categories.json",
-			JSON.stringify( categories, null, "\t" ) + "\n" );
-		done();
-	});
-});
-
 grunt.registerTask( "build", "build-pages build-xml-entries build-xml-categories build-resources build-xml-full" );
 grunt.registerTask( "build-wordpress", "check-modules clean xmllint build" );