Copy removed.txt file to the snapshot correctly

Previously, the code copied the current.txt file to both the
current_api and removed_api properties. This change copies the
removed.txt file to the removed_api property instead.

Bug: 157980685
Test: m nothing
Merged-In: Iad34e91051da43222d22c240c16f50887c43d73e
Change-Id: Iad34e91051da43222d22c240c16f50887c43d73e
(cherry picked from commit 3dbf9fd8)