DO NOT MERGE: Create filename constant for @removed API signature file

CL I8fe27e8c03334f9c90204db1e69447de65a06a38 introduced a new
Doclava-generated file that contains a list of dex signatures of
@removed API. This patch adds a new Makefile variable holding the
name of that file.

Bug: 78182899
Test: make
Merged-In: I20330bd59cc8b3d0ed0fa08d3f1c2be7b8656849
Change-Id: I22474bd0a43b03441a551fbb055ee336665e499a