Revert "mgr/dashboard: pin lxml to fix run-dashboard-tox-make-check failure"

This reverts commit 1f84505.

Signed-off-by: Nizamudeen A <[email protected]>

Author: nizamial09

src/pybind/mgr/dashboard/requirements.txt

@@ -14,5 +14,4 @@ jsonpatch
 grpcio==1.46.5
 grpcio-tools==1.46.5
 jmespath
-lxml==4.8.0  # to fix https://github.com/xmlsec/python-xmlsec/issues/320
 xmltodict