foucalc: Remove Uttley+14 error calculation in colacal.sl

* Uttley+14 calculate the coherence with the full power spectrum
  (noise + signal) in the denominator. This calculation was added in
  commit 4a64f55c.
* This calculation differs from the one in Nowak+99 Eq. 16.,
  Ingram+19 Eq. 21, or Vaughan&Nowak 97 Eq. 8 who divide by the SIGNAL
  power spectrum only.
* Thus, the Uttley+14 coherence will lead to a *smaller* value and
  thus bigger uncertainties on the time lag. That is, Uttley+14
  *overestimate* the uncertainties.
* This commit reverses 4a64f55c: It removes the Uttley+14 calculation.