Upgrading VTU to v1: Remove deprecated `setMethods` calls

What does this MR do

This MR is part of &3856 (closed) and &5102

This change switches from using deprecated setMethods to providing stub with spy :)

Additional changes "while we are here":

• unify nextTick as per gitlab-org/frontend/rfcs#47 (closed)
• remove localVue where possible