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/model/VolumeEncryption.cpp b/model/VolumeEncryption.cpp
index 5b0e73d..e6a55a9 100644
--- a/model/VolumeEncryption.cpp
+++ b/model/VolumeEncryption.cpp
@@ -32,16 +32,16 @@
 enum class VolumeMethod { kFailed, kCrypt, kDefaultKey };
 
 static VolumeMethod lookup_volume_method() {
-    constexpr uint64_t pre_gki_level = 29;
     auto first_api_level =
             android::base::GetUintProperty<uint64_t>("ro.product.first_api_level", 0);
     auto method = android::base::GetProperty("ro.crypto.volume.metadata.method", "default");
     if (method == "default") {
-        return first_api_level > pre_gki_level ? VolumeMethod::kDefaultKey : VolumeMethod::kCrypt;
+        return first_api_level > __ANDROID_API_Q__ ? VolumeMethod::kDefaultKey
+                                                   : VolumeMethod::kCrypt;
     } else if (method == "dm-default-key") {
         return VolumeMethod::kDefaultKey;
     } else if (method == "dm-crypt") {
-        if (first_api_level > pre_gki_level) {
+        if (first_api_level > __ANDROID_API_Q__) {
             LOG(ERROR) << "volume encryption method dm-crypt cannot be used, "
                           "ro.product.first_api_level = "
                        << first_api_level;