Fix encoding of constants (for TPTP provers).
Fix encoding of constants (for TPTP provers).

Locations and labels were leaking into constant definitions, thus
preventing TPTP provers to unify them when equal. Example:
const_shdqproofssldtdtsltest_harnessdtmlwdq_17_23_24sh_3 <> const_3.

ssaavedra/why3,douglas-larocca/why3,jpdeplaix/why3,ssaavedra/why3,jpdeplaix/why3,douglas-larocca/why3,douglas-larocca/why3,jpdeplaix/why3,ssaavedra/why3