Revert "Deep copy grid using xarray.DataArray.copy instead of numpy.copy"

This reverts commit 5a685b2.

Author: weiji14

pygmt/clib/conversion.py

@@ -114,7 +114,7 @@ def dataarray_to_matrix(grid):
         inc = [abs(i) for i in inc]
         grid = grid.sortby(variables=list(grid.dims), ascending=True)
 
-    matrix = as_c_contiguous(grid[::-1].copy(deep=True).data)
+    matrix = as_c_contiguous(grid[::-1].values)
     return matrix, region, inc