Fix missing i = i warning for locals

[Frotty]

Right now this throws a warning:

class A
  var i = 0
  construct()
    this.i = this.i // warning

However this will not:

init
  var i = 0
  i = i // no warning
  print(i)

It works for class members, but not locals. By debugging I found out that in the validator the namelinks for the local scenario don't have the same identity and thus the == check failed. It seems to work with the defs tho.
But idk if this is the 'correct' fix @peq 🤷‍♂️

[coveralls]

Coverage increased (+0.04%) to 61.487% when pulling e13c7df on fix-assignment-no-effect-warning into c33d0ca on master.