It removes the last element of r1 in a rather over the top manner. Basically the same as:
r1(end) = [];
if r1 is a vector.
Edit:
As pointed out by John D'Errico below and added here to correct the answer, since r1 is a matrix rather than a vector
r(:,end) = [];
is the way to achieve the equivalent and remove the final column as oppose to just the final element as the example above would do for a vector.
See John's comment below for more detail.
