fix: remove filelock hard dependency for EL7 compatibility

The code already handles the absence of FileCache gracefully with
try/except blocks (falling back to in-memory cache). Making filelock
a hard requirement in setup.py caused pkg_resources to fail at entry
point loading time on EL7 where filelock>=3.0.0 is unavailable.

Author: dvershinin

setup.py

@@ -14,7 +14,6 @@
     'six',
     'netaddr',
     'cachecontrol',
-    'filelock>=3.0.0',
     'tqdm',
     # required for cf.user.tokens.verify.get() and cf.accounts.get()
     # neither endpoints are available in CentOS 7, thus we rebuild pkg from