Remove deprecated BOARD_BUILD_SYSTEM_ROOT_IMAGE

This variable is always false or empty now, so clean up remaining
references of the variable.

Remove "buildvariant=" kernel commandline as it was used by
system-as-root kernels to determine the system build variant. It is
unsupported now.

Bug: 241346584
Test: Presubmit
Change-Id: I0f97b6e0bf8b03429f65366119ff78f9c7983516
diff --git a/core/main.mk b/core/main.mk
index cdbc3ef..2e39601 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -1846,30 +1846,28 @@
     $(INSTALLED_FILES_JSON_ROOT) \
   )
 
-  ifneq ($(BOARD_BUILD_SYSTEM_ROOT_IMAGE),true)
-    $(call dist-for-goals, droidcore-unbundled, \
-      $(INSTALLED_FILES_FILE_RAMDISK) \
-      $(INSTALLED_FILES_JSON_RAMDISK) \
-      $(INSTALLED_FILES_FILE_DEBUG_RAMDISK) \
-      $(INSTALLED_FILES_JSON_DEBUG_RAMDISK) \
-      $(INSTALLED_FILES_FILE_VENDOR_RAMDISK) \
-      $(INSTALLED_FILES_JSON_VENDOR_RAMDISK) \
-      $(INSTALLED_FILES_FILE_VENDOR_KERNEL_RAMDISK) \
-      $(INSTALLED_FILES_JSON_VENDOR_KERNEL_RAMDISK) \
-      $(INSTALLED_FILES_FILE_VENDOR_DEBUG_RAMDISK) \
-      $(INSTALLED_FILES_JSON_VENDOR_DEBUG_RAMDISK) \
-      $(INSTALLED_DEBUG_RAMDISK_TARGET) \
-      $(INSTALLED_DEBUG_BOOTIMAGE_TARGET) \
-      $(INSTALLED_TEST_HARNESS_RAMDISK_TARGET) \
-      $(INSTALLED_TEST_HARNESS_BOOTIMAGE_TARGET) \
-      $(INSTALLED_VENDOR_DEBUG_BOOTIMAGE_TARGET) \
-      $(INSTALLED_VENDOR_TEST_HARNESS_RAMDISK_TARGET) \
-      $(INSTALLED_VENDOR_TEST_HARNESS_BOOTIMAGE_TARGET) \
-      $(INSTALLED_VENDOR_RAMDISK_TARGET) \
-      $(INSTALLED_VENDOR_DEBUG_RAMDISK_TARGET) \
-      $(INSTALLED_VENDOR_KERNEL_RAMDISK_TARGET) \
-    )
-  endif
+  $(call dist-for-goals, droidcore-unbundled, \
+    $(INSTALLED_FILES_FILE_RAMDISK) \
+    $(INSTALLED_FILES_JSON_RAMDISK) \
+    $(INSTALLED_FILES_FILE_DEBUG_RAMDISK) \
+    $(INSTALLED_FILES_JSON_DEBUG_RAMDISK) \
+    $(INSTALLED_FILES_FILE_VENDOR_RAMDISK) \
+    $(INSTALLED_FILES_JSON_VENDOR_RAMDISK) \
+    $(INSTALLED_FILES_FILE_VENDOR_KERNEL_RAMDISK) \
+    $(INSTALLED_FILES_JSON_VENDOR_KERNEL_RAMDISK) \
+    $(INSTALLED_FILES_FILE_VENDOR_DEBUG_RAMDISK) \
+    $(INSTALLED_FILES_JSON_VENDOR_DEBUG_RAMDISK) \
+    $(INSTALLED_DEBUG_RAMDISK_TARGET) \
+    $(INSTALLED_DEBUG_BOOTIMAGE_TARGET) \
+    $(INSTALLED_TEST_HARNESS_RAMDISK_TARGET) \
+    $(INSTALLED_TEST_HARNESS_BOOTIMAGE_TARGET) \
+    $(INSTALLED_VENDOR_DEBUG_BOOTIMAGE_TARGET) \
+    $(INSTALLED_VENDOR_TEST_HARNESS_RAMDISK_TARGET) \
+    $(INSTALLED_VENDOR_TEST_HARNESS_BOOTIMAGE_TARGET) \
+    $(INSTALLED_VENDOR_RAMDISK_TARGET) \
+    $(INSTALLED_VENDOR_DEBUG_RAMDISK_TARGET) \
+    $(INSTALLED_VENDOR_KERNEL_RAMDISK_TARGET) \
+  )
 
   ifeq ($(PRODUCT_EXPORT_BOOT_IMAGE_TO_DIST),true)
     $(call dist-for-goals, droidcore-unbundled, $(INSTALLED_BOOTIMAGE_TARGET))