ACPICA: Revert "iASL compiler: allow compilation of externals with paths that refer to existing names"

Revert commit 3ddd3f6a (ACPICA: iASL compiler: allow compilation
of externals with paths that refer to existing names; upstream
ACPICA commit 9a252114197409290813bee570e9d53c22b99d32).

This was done in order to allow more relaxed usage of ASL external
declarations.
Signed-off-by: Erik Schmauss <erik.schmauss@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>