Drop useless check for PRODUCT_BOOT_JARS redefinition.

It is not clear why this check exists; it seems to be unneeded, and
removing it does not break any tests.

PRODUCT_BOOT_JARS is a product variable, and therefore handled in a
special way (unlike ordinary Make variables). It is substituted with
a macro that inherits makefile-specific instances of this variable
and merges them into one. This can be seen by adding debug output
to the device-specific makefile.

For example, add the following to device/generic/car/aosp_car_arm.mk:

  $(warning $(PRODUCT_BOOT_JARS))

The build will generate a warning similar to this:

  device/generic/car/aosp_car_arm.mk:21: warning: @inherit:build/make/target/product/aosp_arm.mk @inherit:device/generic/car/emulator/aosp_car_emulator.mk

Test: $(ANDROID_BUILD_TOP)/vendor/google/build/build_test.bash --dist --incremental --shard-count=3 --shard=2
Test: lunch aosp_car_arm    && m
Test: lunch aosp_car_arm64  && m
Test: lunch aosp_car_x86    && m
Test: lunch aosp_car_x86_64 && m
Test: lunch car_x86_64      && m

Change-Id: I061b70b751ca00efa8f215dba8419d2b9e920403
diff --git a/car_product/build/car.mk b/car_product/build/car.mk
index 4814f9a..4a76b5c 100644
--- a/car_product/build/car.mk
+++ b/car_product/build/car.mk
@@ -101,6 +101,7 @@
     libcar-framework-service-jni \
 
 # System Server components
+# Order is important: if X depends on Y, then Y should precede X on the list.
 PRODUCT_SYSTEM_SERVER_JARS += car-frameworks-service
 
 # Boot animation
@@ -184,8 +185,6 @@
     zh_CN zh_HK zh_TW \
     zu_ZA
 
-# should add to BOOT_JARS only once
-ifeq (,$(INCLUDED_ANDROID_CAR_TO_PRODUCT_BOOT_JARS))
 PRODUCT_BOOT_JARS += \
     android.car
 
@@ -198,9 +197,6 @@
 PRODUCT_HIDDENAPI_STUBS_TEST := \
     android.car-test-stubs-dex
 
-INCLUDED_ANDROID_CAR_TO_PRODUCT_BOOT_JARS := yes
-endif
-
 # Disable Prime Shader Cache in SurfaceFlinger to make it available faster
 PRODUCT_PROPERTY_OVERRIDES += \
     service.sf.prime_shader_cache=0