Remove redundant interpolate method for matrixes

[ctessum]

fixes #48

[zsunberg]

@ctessum This is redundant with #47 and can be closed, right?

[ctessum]

I don't think it's redundant.

The function in question is still there: https://github.com/sisl/GridInterpolations.jl/blob/master/src/GridInterpolations.jl#L142

The original function makes a copy of the matrix as Float64s, and #47 changes that to make a copy of the matrix in the same number type as the original matrix, but what I think is called for is just deleting that function entirely, because I don't think there's any reason to make a copy of that array. (But I could be wrong.)

[zsunberg]

oops, sorry! I thought you removed the function in #47, but I didn't look closely.

[zsunberg]

@himanshugupta1009 you mentioned this to me to day. Just wanted to make sure you saw this. Still would be nice to upgrade DenseArray to AbstractArray in another PR like you mentioned.

[himanshugupta1009]

@zsunberg yes, I will make the change and raise a PR today.