Revert "Switch "system/core/base" ref to "system/libbase""

This reverts commit e960b47673416a3af5ad5e012690fc27317a5a3a.

Reason for revert: Looks to have broken sc-d1-dev b/171770441

Change-Id: I958a95c3b57e46cab2ce17c4a4f9e80b45f2ad71
1 file changed