Revert "Makefile: Make sure gcc is built before system.img in developer-* builds"

Summary: This is unnecessary for us and should be reverted for the future inline toolchain builds

Test Plan: Everything works fine without, we're good to go.

Reviewers: randall.rushing, michyprima, rlasalle15, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D187

Change-Id: I4ae5dcb9dc807bec0b8f4b7dfee4090554333f42