ReflectometryISISCreateTransmission creates hidden workspaces if run as a child algorithm

[MialLewis]

Describe the bug
If ran as a child algorithm without an lvalue, ReflectometryISISCreateTransmission creates a hidden workspace in the ADS.

For example, ensuring Show Invisible Workspaces is selected in workbench settings:
ReflectometryISISCreateTransmission(InputRuns='POLREF32130', StoreInADS=False)

Observe a hidden workspace created in the ADS.

I don't think this is the correct behaviour. Child algorithms are routinely those called from other algorithms not via the simpleapi. You'd expect to just be able to be concerned with the scope of the return value, not be concerned about hidden ADS workspaces.

Expected behavior
If the algorithm is run as a child algorithm, no workspaces to be stored in the ADS.

Screenshots

Platform/Version (please complete the following information):

• OS: [e.g. Windows, RHEL 7, Ubuntu, macOS]
• OS Version:
• Mantid Version [e.g. 6.0.0]

Additional context