fix: use shape of grouping and not shape of grouping + shape of signal

[jokasimr]

Fixes #259

This change solves the issue and passes the tests, and it does seem reasonable that we don't care about the shape of the signal when assigning the size of the grouping.

However the removed comment seems to indicate that we do care.

When loading the offending file with this change the instrument/detector_0 entry gets the somewhat cryptic sizes: sizes={'x_pixel_offset': 1280, 'y_pixel_offset': 1280, 'face': 6, 'vertex': 8, 'winding_order': 24, 'time': 0, 'event_time_zero': 1}

So there's still something wrong here.

[jokasimr]

Here's the instrument/detector_panel_0:

DataGroup(sizes={'x_pixel_offset': 1280, 'y_pixel_offset': 1280, 'face': 6, 'vertex': 8, 'winding_order': 24, 'time': 0, 'event_time_zero': 1}, keys=[
    data: DataArray({'x_pixel_offset': 1280, 'y_pixel_offset': 1280}),
    depends_on: TransformationChain(parent='/entry/instrument/detector_panel_1', value='/entry/instrument/detector_panel_1/transformations/orientation', transformations=DataGroup(sizes={'time': 0}, keys=[
    /entry/instrument/detector_panel_1/transformations/orientation: Transform({}),
    /entry/instrument/detector_panel_1/transformations/axis6: Transform({'time': 0}),
    /entry/instrument/detector_panel_1/transformations/axis5: Transform({'time': 0}),
    /entry/instrument/detector_panel_1/transformations/axis4: Transform({'time': 0}),
    /entry/instrument/detector_panel_1/transformations/axis3: Transform({'time': 0}),
    /entry/instrument/detector_panel_1/transformations/axis2: Transform({'time': 0}),
    /entry/instrument/detector_panel_1/transformations/axis1: Transform({'time': 0}),
    /entry/instrument/detector_panel_1/transformations/stageZ: Transform({'time': 0}),
])),
    detector_number: Variable({'x_pixel_offset': 1280, 'y_pixel_offset': 1280}),
    efu_publication: DataGroup(4, {}),
    geometry: DataGroup(3, {'face': 6, 'vertex': 8, 'winding_order': 24}),
    transformations: DataGroup(8, {'time': 0}),
    x_pixel_offset: Variable({'x_pixel_offset': 1280}),
    y_pixel_offset: Variable({'y_pixel_offset': 1280}),
    z_pixel_offset: Variable({'event_time_zero': 1}),

The only issue I see there is: z_pixel_offset: Variable({'event_time_zero': 1}),