ci(codecov): remove codecov badge and deprecate codecov.yml

Codecov integration is no longer active. Coverage is now handled by
JaCoCo + madrapps/jacoco-report in pr-build.yml.

- Remove stale codecov badge from README.md
- Add DEPRECATED header to codecov.yml for clarity

README.md

@@ -8,7 +8,6 @@
 
 <p align="center">
   <a href="https://discord.gg/hqKvyAM"><img src="https://img.shields.io/badge/chat-on%20discord-7289da.svg"></a>
-  <a href="https://codecov.io/gh/tronprotocol/java-tron"><img src="https://codecov.io/gh/tronprotocol/java-tron/branch/develop/graph/badge.svg" /></a>
   <a href="https://github.com/tronprotocol/java-tron/issues"><img src="https://img.shields.io/github/issues/tronprotocol/java-tron.svg"></a>
   <a href="https://github.com/tronprotocol/java-tron/pulls"><img src="https://img.shields.io/github/issues-pr/tronprotocol/java-tron.svg"></a>
   <a href="https://github.com/tronprotocol/java-tron/graphs/contributors"><img src="https://img.shields.io/github/contributors/tronprotocol/java-tron.svg"></a>

codecov.yml

@@ -1,3 +1,7 @@
+# DEPRECATED: Codecov integration is no longer active.
+# Coverage is now handled by JaCoCo + madrapps/jacoco-report in pr-build.yml.
+# This file is retained for reference only and can be safely deleted.
+
 # Post a Codecov comment on pull requests. If don't need comment, use comment: false, else use following
 comment: false
 #comment: