drop_coordinates behaviour contradicts documentation #3353

Describe the bug

According to the documentation, satpy.composites.core.CompositeBase.drop_coordinates drops coordinates that do not correspond to any dimension:

In reality, it also drops coordinates that do correspond to a dimension.

To Reproduce

import numpy as np
import xarray as xr
import satpy.composites.core

ds = xr.DataArray(
        np.arange(3*4).reshape(3, 4),
        dims=("y", "x"),
        coords={"time": xr.DataArray(
            np.arange(3).reshape(3), dims=("y",))})

print(ds.coords)

# this dataset has a coordinate (time) corresponding to a dimension (y)

ds_new = satpy.composites.core.CompositeBase.drop_coordinates([ds])[0]

# but the coordinate is still dropped

print(ds_new.coords)

Expected behaviour

I'm not sure what the intention is of the code.

I expect that either

• the documentation accurate describes that coordinates are dropped even if they correspond to a dimension, unless that dimension has the same name as the coordinate, or
• this coordinate is retained, as is documented.

Actual results

The coordinate is dropped:

Coordinates:
    time     (y) int64 24B 0 1 2
Coordinates:
    *empty*

Environment Info:

• OS: openSUSE Leap 15.6
• Satpy Version: v0.60.0

Additional context

This behaviour was originally introduced in #796. It breaks #3168, which intends to retain time information.