Revert "Consistently use either "boot" or "apex" boot image as the default."

This reverts commit 48b3b3c71f76fa05de191b8460a186e9dbcc36bf.

Reason for revert: breaks emulator

BUG: 146558375

Change-Id: I2af3d11ad9a014b0d73a73540bc814f245bc6418
diff --git a/java/dexpreopt_config.go b/java/dexpreopt_config.go
index d578b67..91e0dfb 100644
--- a/java/dexpreopt_config.go
+++ b/java/dexpreopt_config.go
@@ -234,7 +234,7 @@
 	return *genBootImageConfigs(ctx)[artBootImageName]
 }
 
-func frameworkBootImageConfig(ctx android.PathContext) bootImageConfig {
+func defaultBootImageConfig(ctx android.PathContext) bootImageConfig {
 	return *genBootImageConfigs(ctx)[frameworkBootImageName]
 }
 
@@ -242,14 +242,6 @@
 	return *genBootImageConfigs(ctx)[apexBootImageName]
 }
 
-func defaultBootImageConfig(ctx android.PathContext) bootImageConfig {
-	if dexpreoptGlobalConfig(ctx).UseApexImage {
-		return apexBootImageConfig(ctx)
-	} else {
-		return frameworkBootImageConfig(ctx)
-	}
-}
-
 func defaultBootclasspath(ctx android.PathContext) []string {
 	return ctx.Config().OnceStringSlice(defaultBootclasspathKey, func() []string {
 		global := dexpreoptGlobalConfig(ctx)