* Move tidyType and friends from TcType to TypeRep
  (It was always wrong to have it in TcType.)

* Move mkCoAxBranch and friends from FamInst to Coercion

* Move pprCoAxBranch and friends from FamInstEnv to Coercion

No change in functionality, though there might be a little
wibble in error message output, because I combined two different
functions both called pprCoAxBranch!