Purging shape key data with Python

Question

I'm trying to purge all data left by multiple appends through Python in order to get a clean blend file after my script ran.

I found a way that work for all data except shape keys

#Delete all data
datalist = [
    bpy.data.meshes, 
    bpy.data.curves,
    bpy.data.materials,
    bpy.data.images,
    bpy.data.shape_keys]

for data in datalist:
    for x in data.keys():
        if data[x].users == 0:
            data.remove(data[x])

Turns out bpy.data.shape_keys has no attribute .remove()

No idea why, but how can I get rid of those useless shape keys?