Remove version field from composer.json

The version field causes composer validate --strict to fail with a warning.
Version is determined by git tags instead.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

composer.json

@@ -1,7 +1,6 @@
 {
     "name": "magdev/wc-tier-package-prices",
     "description": "WooCommerce plugin for tier pricing and package prices with Twig templates",
-    "version": "1.4.0",
     "type": "wordpress-plugin",
     "license": "GPL-2.0-or-later",
     "authors": [