app: refactor: drop the last findings reference from the manifest resources

network_security_config.xml still pointed at FINDINGS_APP_VULN V13. It sits
outside the Kotlin sources so the previous pass missed it. The comment already
explains why cleartext is blocked app-wide, so only the pointer goes.

Signed-off-by: ravindu644 <droidcasts@protonmail.com>

Author: ravindu644

Android/app/src/main/res/xml/network_security_config.xml

@@ -3,7 +3,7 @@
   Droidspaces talks only to HTTPS endpoints (the rootfs manifest + downloads).
   Block all cleartext traffic app-wide so a repackage, a lowered targetSdk, or a
   user-added http:// custom repo cannot silently expose the rootfs supply chain
-  to MITM. See FINDINGS_APP_VULN V13.
+  to MITM.
 -->
 <network-security-config>
     <base-config cleartextTrafficPermitted="false" />