Unspecified expression degree does not throw

[Jan Blechta]

Defining expression without degree/element specified has been deprecated. But deprecation has been removed without turning this into error. Following MWE shows that such expression can be used without an error

from dolfin import *
mesh = UnitSquareMesh(1,1)
V = FunctionSpace(mesh,'CG',1)
f = Expression('x[0]*x[1]')
project(f,V)