Remove inherintence of supervisory kind for invariants.

Kindless invariants for synthesis were deprecated on the 11th of October 2015. We should no longer support it.

Synthesizing the following specification:

plant A:
  disc int[0..3] X = 3;
  location:
    initial; marked;
end

requirement R:
  location:
    initial; marked;
    invariant A.X != 2;
end

Gives the following warning.

WARNING: File "issue.cif": Semantic warning at line 10, column 19: Invariant does not specify a supervisory kind and thus implicitly inherits supervisory kind "requirement" from automaton "R". This is deprecated. Please explicitly specify the kind before the "invariant" keyword.