Remove dib-lint flake8 requirement
Remove dib-lint flake8 requirement

With the dependent change, this should be requested by
diskimage-builder itself.

Change-Id: Id45c0dfcae86672e4a0c6cdc7c057d9aa6d291b1
Depends-On: I3052f860cebc66844cd21f34be64aea8474d2248

Tesora/tesora-project-config,openstack-infra/project-config,noorul/os-project-config,dongwenjuan/project-config,dongwenjuan/project-config,noorul/os-project-config,openstack-infra/project-config,Tesora/tesora-project-config