Don't install files for the virt APEX onto the system partition

Previously, since the virt APEX is configured as non-updatable, the
build system enabled the symlink optimization where files are installed
directly to the system partition and the APEX has symlinks to the files.
However, this forced us to add those files to
PRODUCT_ARTIFACT_PATH_REQUIREMENT_ALLOWED_LIST as we install the APEX
conditionally - because the inclusion of the APEX is done by a product,
not by the core build system.

This change works around the problem by marking the APEX
non-installable. Then the build system doesn't enable the symlink
optimization.

Bug: 207336449
Test: watch TH

Change-Id: I020ae84defe5ce03f0fc2226f2fbd42a5823861e

apex/Android.bp

@@ -16,6 +16,9 @@ apex {
     // TODO(jiyong): make it updatable
     updatable: false,
     platform_apis: true,
+    // b/207336449: this is to turn the symlink optimization off while keeping this APEX
+    // non-updatable. Can be removed when `updatable` becomes true.
+    installable: false,
 
     system_ext_specific: true,
 

apex/product_packages.mk

@@ -25,7 +25,6 @@ PRODUCT_PACKAGES += \
 
 # TODO(b/207336449): Figure out how to get these off /system
 PRODUCT_ARTIFACT_PATH_REQUIREMENT_ALLOWED_LIST := \
-    system/lib64/libgfxstream_backend.so \
     system/framework/oat/%@service-compos.jar@classes.odex \
     system/framework/oat/%@service-compos.jar@classes.vdex \