message: refactor(api): Remove obsolete todo for flow rates
diff: @@ -23,10 +23,6 @@ class VolumeMixin(BaseModel):
  gt=0,
  )
  - # todo(mm, 2021-03-26): This class or one of its subclasses should have a
  - # field for liquid flow rate in microliters per second.
  - # See Opentrons/opentrons#4837 for terminology concerns.
  -
  class FlowRateMixin(BaseModel):
  """Mixin for command requests that take a flow rate."""
  