Remove SOONG_CONFIG_art_module_source_build fallback

Usages of SOONG_CONFIG_art_module_source_build have been
replaced with ART_MODULE_BUILD_FROM_SOURCE now.

Bug: 220940864
Test: Presubmits
Change-Id: Ibe2115e385efe3ec02cd66ff3c5aca73ce986508
diff --git a/core/android_soong_config_vars.mk b/core/android_soong_config_vars.mk
index 77260e6..99acdab 100644
--- a/core/android_soong_config_vars.mk
+++ b/core/android_soong_config_vars.mk
@@ -59,12 +59,6 @@
   MODULE_BUILD_FROM_SOURCE := $(BRANCH_DEFAULT_MODULE_BUILD_FROM_SOURCE)
 endif
 
-# TODO(b/220940864): Remove when build scripts have been changed to use
-# ART_MODULE_BUILD_FROM_SOURCE instead of SOONG_CONFIG_art_module_source_build
-ifneq (,$(SOONG_CONFIG_art_module_source_build))
-  ART_MODULE_BUILD_FROM_SOURCE := $(SOONG_CONFIG_art_module_source_build)
-endif
-
 ifneq (,$(ART_MODULE_BUILD_FROM_SOURCE))
   # Keep an explicit setting.
 else ifneq (,$(findstring .android.art,$(TARGET_BUILD_APPS)))