[display_manager] Remove flag for deprecated package reference by name

This package is used only in the context of the fidl service, where it is
fully referenced by url in the service mapping.

Fixes: CF-453
Test: manual
Change-Id: Ifdade9dfe1de1df31c5f70c4a3a65af1612f25c1
diff --git a/bin/display_manager/BUILD.gn b/bin/display_manager/BUILD.gn
index 6cdd1a4..dc609f5 100644
--- a/bin/display_manager/BUILD.gn
+++ b/bin/display_manager/BUILD.gn
@@ -26,8 +26,6 @@
 }
 
 package("display_manager") {
-  deprecated_bare_package_url = "//build"
-
   deps = [
     ":bin",
   ]