Don't create SDK variants for native bridge modules

Native bridge modules never need to build against NDK stubs, so
don't create SDK variants.  Also clear the sdk_version property
for modules that don't have SDK variants so that later code doesn't
use it to trigger SDK behaviors.

Test: m checkbuild
Change-Id: I1920fa82e9fab06235f01a62624382efa16cc6e3
diff --git a/cc/cc.go b/cc/cc.go
index f45b654..d719006 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -1046,7 +1046,8 @@
 }
 
 func (c *Module) canUseSdk() bool {
-	return c.Os() == android.Android && !c.UseVndk() && !c.InRamdisk() && !c.InRecovery() && !c.InVendorRamdisk()
+	return c.Os() == android.Android && c.Target().NativeBridge == android.NativeBridgeDisabled &&
+		!c.UseVndk() && !c.InRamdisk() && !c.InRecovery() && !c.InVendorRamdisk()
 }
 
 func (c *Module) UseSdk() bool {