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/classpath_fragment.go b/java/classpath_fragment.go
index 45e6175..cf81ddb 100644
--- a/java/classpath_fragment.go
+++ b/java/classpath_fragment.go
@@ -130,13 +130,13 @@
 				if s, ok := m.(*SdkLibrary); ok {
 					// TODO(208456999): instead of mapping "current" to latest, min_sdk_version should never be set to "current"
 					if s.minSdkVersion.Specified() {
-						if s.minSdkVersion.IsCurrent() {
+						if s.minSdkVersion.ApiLevel.IsCurrent() {
 							jar.minSdkVersion = ctx.Config().DefaultAppTargetSdk(ctx).String()
 						} else {
-							jar.minSdkVersion = s.minSdkVersion.String()
+							jar.minSdkVersion = s.minSdkVersion.ApiLevel.String()
 						}
 					}
-					if s.maxSdkVersion.ApiLevel.Specified() {
+					if s.maxSdkVersion.Specified() {
 						if s.maxSdkVersion.ApiLevel.IsCurrent() {
 							jar.maxSdkVersion = ctx.Config().DefaultAppTargetSdk(ctx).String()
 						} else {