Pi-Heif: remove avif keyword

pi-heif/setup.cfg

@@ -6,7 +6,7 @@ long_description_content_type = text/markdown
 url = https://github.com/bigcat88/pillow_heif
 author = Alexander Piskun
 author_email = bigcat88@users.noreply.github.com
-keywords = heif, heic, avif, pillow
+keywords = heic, heif, pillow
 classifiers =
     Development Status :: 5 - Production/Stable
     Intended Audience :: Developers