Set PRODUCT_SHIPPING_API_LEVEL in gsi_release.mk

Set PRODUCT_SHIPPING_API_LEVEL to the latest value (instead of empty) so
that GSIs are always built with the latest build system default configs,
such as PRODUCT_FULL_TREBLE := true and
PRODUCT_ENFORCE_PRODUCT_PARTITION_INTERFACE := true.

Bug: 177495407
Test: Presubmit build_test
Change-Id: Iabd67656c5ed1de8327c40f0f9f604841f24764b
diff --git a/target/product/gsi_release.mk b/target/product/gsi_release.mk
index 2c74ce0..34821b6 100644
--- a/target/product/gsi_release.mk
+++ b/target/product/gsi_release.mk
@@ -31,8 +31,10 @@
     system/product/% \
     system/system_ext/%
 
-# Split selinux policy
-PRODUCT_FULL_TREBLE_OVERRIDE := true
+# GSI should always support up-to-date platform features.
+# Keep this value at the latest API level to ensure latest build system
+# default configs are applied.
+PRODUCT_SHIPPING_API_LEVEL := 30
 
 # Enable dynamic partition size
 PRODUCT_USE_DYNAMIC_PARTITION_SIZE := true