Remove TODO about GCC as we're not going to add it.

Bug: 132428451
Change-Id: I8ac820461690fca034847ace09672717d2784309
diff --git a/BUILD.gn b/BUILD.gn
index 0e766ae..f18517e 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -15,8 +15,6 @@
 import("//build/toolchain/embedded.gni")
 import("//build/toolchain/host.gni")
 
-# TODO: add a gcc-4.9 or above prebuilt to check the gcc build too?
-
 group("root") {
   deps = [
     "//src:hafnium(:aem_v8a_fvp_clang)",