doc: remove egg fragment from dev/developer_guide/running-tests-locally

doc: remove egg fragment from dev/developer_guide/running-tests-locally

DEPRECATION: git+https://github.com/ceph/teuthology#egg=teuthology
[test] contains an egg fragment with a non-PEP 508 name pip 25.0 will enforce
this behaviour change. A possible replacement is to use the req @ url syntax,
and remove the egg fragment. Discussion can be found at
https://github.com/pypa/pip/issues/11617

Signed-off-by: Dhairya Parmar <dparmar@redhat.com>
(cherry picked from commit 1f78a32a1822fea1a56a88215e452b730b7672c7)