Update source position and name for IN4 spectrometer

[soininen]

This PR moves the source of the IN4 spectrometer at ILL from the rather arbitrary z = -2m to the position of the Fermi chopper at z = -0.675.

To test:

Check that the L1 distance for IN4 is 0.675 meters instead of the earlier 2m.

Fixes #18679.

Does not need to be in the release notes.

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[KarlPalmen]

Source has been moved to Fermi-chopper at 0.675 and moderator (the old source) has been removed and there are no references to it in the IDF file.

[KarlPalmen]

Instrument IN4 loaded with out error and then displayed OK without error.

[KarlPalmen]

subject to builds working.