bug: flopy creates FTL file using MF6 + MT3D USGS: causing crash

[lukatas]

Describe the bug
MT3D-USGS does not run with a MF6 model in flopy

When writing the input for MT3D-USGS the .ftl file is still in the .mt_nam file. There should not be a linking file when using MF6, this causes MT3D-USGS to crash.
However, when using ModelMuse the .mt_nam file is written correctly whithout the linking file. So the problem is specific to flopy.
This could be linked to issue #775 .

Flopy version: 3.3.6
Modelmuse: 5.1.1.0
MF6: 6.3.0
MT3D-USGS: 1.1.0

[robinthibaut]

I have the same problem, it is impossible to run MT3DMS-USGS with MF6 without workarounds.