chore: remove redundant license classifier from pyproject.toml

The license expression field (PEP 639) supersedes the classifier.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "hbd"
-version = "5.3.4"
+version = "5.3.5"
 description = "Heartbeat monitoring system — client (hbc) and server (hbd)"
 readme = "README.md"
 requires-python = ">=3.11"
@@ -26,7 +26,6 @@ classifiers = [
   "Operating System :: POSIX :: BSD",
   "Topic :: System :: Monitoring",
   "Topic :: System :: Networking :: Monitoring",
-  "License :: OSI Approved :: MIT License",
 ]
 
 [project.urls]