fix: remove image key so HA builds from Dockerfile with entrypoint

The image: key forced HA to pull upstream technitium/dns-server directly,
bypassing the Dockerfile entirely — so the entrypoint.sh persistence fix
was never applied. Removing it makes HA build the image locally.

technitium_dns/config.yaml

@@ -1,5 +1,5 @@
 name: Technitium DNS
-version: 15.4.0
+version: 15.4.3
 slug: technitium_dns
 description: Technitium DNS Server add-on for Home Assistant
 arch:
@@ -40,5 +40,4 @@ schema:
   timezone: str
   enable_https: bool
   tls_cert_pfx_path: str?
-  tls_cert_pfx_password: password?
-image: technitium/dns-server
+  tls_cert_pfx_password: password?