Drop urllib3 upper bound

This was added in kubernetes-client@27459d5.

Note that google-auth now requires urllib3>=2 in googleapis/google-auth-library-python#1389

(I'm also not sure that I follow the logic in kubernetes-client#2105, since dependency resolvers will be able to work it out)

requirements.txt

@@ -9,4 +9,4 @@ websocket-client>=0.32.0,!=0.40.0,!=0.41.*,!=0.42.* # LGPLv2+
 requests # Apache-2.0
 requests-oauthlib # ISC
 oauthlib>=3.2.2 # BSD
-urllib3>=1.24.2,<2.0  # MIT
+urllib3>=1.24.2  # MIT