vold: use __ANDROID_API_Q__ instead of pre_gki_level

The name "pre_gki_level" is causing some confusion because not all
devices launching with Android R are subject to the GKI requirement.
(See b/161563110#comment11.)  E.g., devices that use a 4.14-based kernel
are exempt from GKI.  However, the encryption requirements still apply.

Just use __ANDROID_API_Q__ directly instead.

No change in behavior.

Change-Id: Id02ae1140845ac1ae7cf78be4e57fe34da028abf
diff --git a/MetadataCrypt.cpp b/MetadataCrypt.cpp
index ca2813d..c61132c 100644
--- a/MetadataCrypt.cpp
+++ b/MetadataCrypt.cpp
@@ -283,10 +283,9 @@
         return false;
     }
 
-    constexpr unsigned int pre_gki_level = 29;
     unsigned int options_format_version = android::base::GetUintProperty<unsigned int>(
             "ro.crypto.dm_default_key.options_format.version",
-            (GetFirstApiLevel() <= pre_gki_level ? 1 : 2));
+            (GetFirstApiLevel() <= __ANDROID_API_Q__ ? 1 : 2));
 
     CryptoOptions options;
     if (options_format_version == 1) {