Revert "Update min_sdk_version from SdkSpec to ApiLevel"

Revert submission 2457063

Reason for revert: Broken udc-dev

Reverted changes: /q/submissionid:2457063

Change-Id: Id6349fc1318877044af713c914a0afd437d3d2d5
diff --git a/java/hiddenapi_modular.go b/java/hiddenapi_modular.go
index 445ca1e..be4a48e 100644
--- a/java/hiddenapi_modular.go
+++ b/java/hiddenapi_modular.go
@@ -1278,7 +1278,7 @@
 	uncompressDex bool
 
 	// The minimum sdk version that the dex jar will be used on.
-	minSdkVersion android.ApiLevel
+	minSdkVersion android.SdkSpec
 }
 
 // bootDexInfoByModule is a map from module name (as returned by module.Name()) to the boot dex