Clear resource_export_package outside conditionals

$(resource_export_package) is used by package_internal.mk outside
ifeq ($(need_compile_res),true), but only cleared inside the
conditional.  This causes unnecessary dependencies to be added
to an old value of $(resource_export_package).  In rare cases,
the dependency can be on itself, causing a dependency loop.

Bug: 71571462
Test: m checkbuild
Change-Id: I9fda7fe3bf9d208ad4ba2f8cdb184034bf43f044