Mitch gets a better idea to deal with soft limits (i.e. min/max values
different from the property min/max) applied to a spin scale created by
gimp_prop_spin_scale_new().
So let's just remove the current implementation (using locale data on
the GimpConfig object). The symmetry spin scales are back with crazy
huge maximums, which makes quite a horrible GUI, but this is only
temporary until Mitch commits his new implementation.