Remove transitional GN build variable.

build/config/BUILDCONFIG.gn

Index: build/config/BUILDCONFIG.gn
diff --git a/build/config/BUILDCONFIG.gn b/build/config/BUILDCONFIG.gn
index 71161b086acea93df649bbdedb8d299845338d5a..8bda2cd71ecd7fb4e20f1b1004271bd1f447f481 100644
--- a/build/config/BUILDCONFIG.gn
+++ b/build/config/BUILDCONFIG.gn
@@ -158,22 +158,6 @@ declare_args() {
 # be non-global.
 using_new_global_compiler_configs = true
 
-# To assist in a multi-sided landing of updating the default optimization
-# config. When false, this file sets up the default optimization config to be
-# either "no_optimize" (debug) or "optimize" (release). When true it will
-# always set the config "default_optimization".
-#
-# TODO(brettw) remove this when all repos are updated.
-using_new_optimization_config = true
-
-# To assist in a multi-sided landing of updating the default optimization
-# config. When false, this file sets up the default optimization config to be
-# either "no_optimize" (debug) or "optimize" (release). When true it will
-# always set the config "default_optimization".
-#
-# TODO(brettw) remove this when all repos are updated.
-using_new_optimization_config = true
-
 # =============================================================================
 # OS DEFINITIONS
 # =============================================================================