Promote the NewApi check to an error again

Now that all existing cases have been baselined.

Ignore-AOSP-First: Requires a LSC that is difficult to do across branches.
Bug: 268261262
Test: m lint-check
Change-Id: I413f86ff7a1f33564465f3ba9cd52924a4242901
diff --git a/java/lint.go b/java/lint.go
index c3d723b..91e22a4 100644
--- a/java/lint.go
+++ b/java/lint.go
@@ -319,12 +319,7 @@
 	cmd.FlagWithInput("@",
 		android.PathForSource(ctx, "build/soong/java/lint_defaults.txt"))
 
-	if l.compileSdkKind == android.SdkPublic {
-		cmd.FlagForEachArg("--error_check ", l.extraMainlineLintErrors)
-	} else {
-		// TODO(b/268261262): Remove this branch. We're demoting NewApi to a warning due to pre-existing issues that need to be fixed.
-		cmd.FlagForEachArg("--warning_check ", l.extraMainlineLintErrors)
-	}
+	cmd.FlagForEachArg("--error_check ", l.extraMainlineLintErrors)
 	cmd.FlagForEachArg("--disable_check ", l.properties.Lint.Disabled_checks)
 	cmd.FlagForEachArg("--warning_check ", l.properties.Lint.Warning_checks)
 	cmd.FlagForEachArg("--error_check ", l.properties.Lint.Error_checks)