Update max_sdk_version from SdkSpec to ApiLevel

max_sdk_version signifies device version and does not need an sdkKind to
describe it fully. Update the type and cleanup existing usages. As a
side benefit, we also get better error handling since users can no
longer enter something like `public_30` as a valid max_sdk_version in bp
files

Bug: 208456999
Test: no change in ninja file (this should be a no-op)
Test: TH
Change-Id: I304b5ad802bde200137d8e225182828dfd6f7227
diff --git a/java/aar.go b/java/aar.go
index f162a17..47e6efa 100644
--- a/java/aar.go
+++ b/java/aar.go
@@ -721,8 +721,8 @@
 	return a.SdkVersion(ctx).ApiLevel
 }
 
-func (a *AARImport) ReplaceMaxSdkVersionPlaceholder(ctx android.EarlyModuleContext) android.SdkSpec {
-	return android.SdkSpecFrom(ctx, "")
+func (a *AARImport) ReplaceMaxSdkVersionPlaceholder(ctx android.EarlyModuleContext) android.ApiLevel {
+	return android.SdkSpecFrom(ctx, "").ApiLevel
 }
 
 func (a *AARImport) TargetSdkVersion(ctx android.EarlyModuleContext) android.ApiLevel {