Remove ro.apex.updatable=false in GSI

Originally, GSI forced disable APEX and always contains apex
packages in flattern format. This patch remove the enforcement,
and APEX updateble is enabled according to ro.apex.updatable in
vendor.

Bug: 145245545
Test: build aosp_arm64-userdebug, check the property in system
Change-Id: I9cc943d7b2a30d037a2c1c137dad1233c1e3f57e