Add genrules for merged removed.txt files

No diffs vs monoliths.

Bug: 169034951
Test: for p in "" "system-" "module-lib-"; do
  for t in "current" "removed"; do
      echo "${p}${t}:"
      echo "$(diff -u0 \
          <($CANON frameworks/base/api/${p}${t}.txt | sort) \
          <($CANON out/soong/.intermediates/frameworks/base/api/frameworks-base-api-${p}${t}-merged.txt/gen/${p}${t}.txt | sort))"
  done
done

Change-Id: Id97b88b7d8e4c0b0e372e30658c48436427dbe7c