Remove remains of old depend target.

Makefile

src/Makefile

src/backend/Makefile

src/backend/access/Makefile

src/backend/access/common/Makefile

src/backend/access/gin/Makefile

src/backend/access/gist/Makefile

src/backend/access/hash/Makefile

src/backend/access/heap/Makefile

src/backend/access/index/Makefile

src/backend/access/nbtree/Makefile

src/backend/bootstrap/Makefile

src/backend/commands/Makefile

src/backend/executor/Makefile

src/backend/lib/Makefile

src/backend/libpq/Makefile

src/backend/main/Makefile

src/backend/nodes/Makefile

src/backend/optimizer/Makefile

src/backend/optimizer/geqo/Makefile