Update license information according to PEP 639

Author: jlaine

pyproject.toml

@@ -7,14 +7,13 @@ name = "pylibsrtp"
 description = "Python wrapper around the libsrtp library"
 readme = "README.rst"
 requires-python = ">=3.9"
-license = { text = "BSD-3-Clause" }
+license = "BSD-3-Clause"
 authors = [
     { name = "Jeremy Lainé", email = "[email protected]" },
 ]
 classifiers = [
     "Development Status :: 5 - Production/Stable",
     "Intended Audience :: Developers",
-    "License :: OSI Approved :: BSD License",
     "Operating System :: OS Independent",
     "Programming Language :: Python",
     "Programming Language :: Python :: 3",