Move AllowMissingDependencies handling into processMainCert

I046d75dbbd4f21f4a2b6851f558e430e9879fcff fixed android_app modules
with missing certificate dependencies when AllowMissingDependencies
was set, but the same problem can occur in android_app_import and
android_rro modules.  Move the AllowMissingDependencies handling
into processMainCert so that it applies to all of them.

Bug: 246649647
Test: TestAppImportMissingCertificateAllowMissingDependencies
Change-Id: Ic7dd3e61e0e3af15c53b583cf680b1e52394a018
diff --git a/java/rro.go b/java/rro.go
index c12e748..3a92b0c 100644
--- a/java/rro.go
+++ b/java/rro.go
@@ -146,7 +146,7 @@
 
 	// Sign the built package
 	_, _, certificates := collectAppDeps(ctx, r, false, false)
-	certificates = processMainCert(r.ModuleBase, String(r.properties.Certificate), certificates, ctx)
+	r.certificate, certificates = processMainCert(r.ModuleBase, String(r.properties.Certificate), certificates, ctx)
 	signed := android.PathForModuleOut(ctx, "signed", r.Name()+".apk")
 	var lineageFile android.Path
 	if lineage := String(r.properties.Lineage); lineage != "" {
@@ -156,7 +156,6 @@
 	rotationMinSdkVersion := String(r.properties.RotationMinSdkVersion)
 
 	SignAppPackage(ctx, signed, r.aapt.exportPackage, certificates, nil, lineageFile, rotationMinSdkVersion)
-	r.certificate = certificates[0]
 
 	r.outputFile = signed
 	partition := rroPartition(ctx)