refactor(basis): remove NSurf NURBS surface basis

Drop unmaintained tensor-product surface NURBS tied to removed NURBS helpers.

src/basis/nurbs_surface.jl

@@ -1,47 +0,0 @@
-# This file is a part of JuliaFEM.
-# License is MIT: see https://github.com/JuliaFEM/jl/blob/master/LICENSE
-
-mutable struct NSurf <: AbstractBasis{2}
-    order_u :: Int
-    order_v :: Int
-    knots_u :: Vector{Float64}
-    knots_v :: Vector{Float64}
-    weights :: Matrix{Float64}
-end
-
-function NSurf()
-    NSurf(1, 1,
-        [-1.0, -1.0, 1.0, 1.0],
-        [-1.0, -1.0, 1.0, 1.0],
-        ones(2, 2))
-end
-
-function length(basis::NSurf)
-    nu = length(basis.knots_u) - basis.order_u - 1
-    nv = length(basis.knots_v) - basis.order_v - 1
-    return nu*nv
-end
-
-function size(basis::NSurf)
-    return (2, length(basis))
-end
-
-function eval_basis!(basis::NSurf, N::Vector, xi::Vec{2})
-    pu = basis.order_u
-    pv = basis.order_v
-    tu = basis.knots_u
-    tv = basis.knots_v
-    w = basis.weights
-    nu = length(tu)-pu-1
-    nv = length(tv)-pv-1
-    u, v = xi
-    n = 1
-    for i=1:nu
-        for j=1:nv
-            N[n] = w[i,j]*NURBS(i,pu,u,tu)*NURBS(j,pv,v,tv)
-            n += 1
-        end
-    end
-    N ./= sum(N)
-    return N
-end