Drop Python 3.5 from Trove classifier metadata. (#9782)

* Drop Python 3.5 from Trove classifier metadata.

Signed-off-by: Dan Callahan <danc@element.io>

changelog.d/9782.misc

+Synapse now requires Python 3.6 or later. It also requires Postgres 9.6 or later or SQLite 3.22 or later.

setup.py

@@ -129,7 +129,6 @@ setup(
         "Topic :: Communications :: Chat",
         "License :: OSI Approved :: Apache Software License",
         "Programming Language :: Python :: 3 :: Only",
-        "Programming Language :: Python :: 3.5",
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",