Don't know if there's an updated, more elegant way to do this, but the solution here does it in a roundabout way, which works.
% create the polar plot, and store the line's handle
p = polar((0:99)*pi/100, (0:99)/100);
% find all of the lines in the polar plot
h = findall(gcf,'type','line');
% remove the handle for the polar plot line from the array
h(h == p) = [];
% delete all other lines
delete(h);
% find all of the text objects in the polar plot
t = findall(gcf,'type','text');
% delete the text objects
delete(t);
