[PWGLF] Use the O2 charged pion mass constant in the K1 ML feature builder

The K1 ML feature contract SHA covers the 125 feature names and the three
projection index lists only, so switching the pion mass from the local
literal to o2::constants::physics::MassPionCharged does not change the
contract identity. Feature values change at the 1e-8 relative level for
the pair masses; exports written with the previous literal are therefore
not byte-identical to new exports.

Author: BongHwi

PWGLF/Core/K1MlFeatures.h

@@ -744,11 +744,6 @@ static_assert(detail::isStrictlyIncreasingBelow(RelationalV1Projection, NMasterF
 static_assert(detail::isStrictlyIncreasingBelow(SubstructureV1Projection, NMasterFeatures), "SubstructureV1 projection indices must be strictly increasing and below NMasterFeatures");
 inline constexpr std::string_view FeatureContractSha256 = "39f38ece001581d8ebf57392fad045759a63ba49f57c411b9b566d7c1cc58b8a";
 
-// The kaon mass is the O2 constant (exactly 0.493677). The pion mass keeps the
-// frozen feature-contract literal; O2 MassPionCharged differs (0.1395704).
-inline constexpr double K1ChargedKaonMassGeV = o2::constants::physics::MassKaonCharged;
-inline constexpr double ChargedPionMassGeV = 0.13957039; // o2-linter: disable=pdg/explicit-mass (frozen feature contract value; O2 MassPionCharged is 0.1395704)
-
 inline FeaturePack buildMasterFeatures(CandidateSnapshot const& candidate)
 {
   FeaturePack pack;
@@ -769,7 +764,7 @@ inline FeaturePack buildMasterFeatures(CandidateSnapshot const& candidate)
 
   std::array<detail::Kinematics, NCandidateTracks> kin{};
   for (std::size_t i = 0; i < NCandidateTracks; ++i) {
-    if (!detail::getKinematics(candidate.tracks[i], i == 0 ? K1ChargedKaonMassGeV : ChargedPionMassGeV, kin[i])) {
+    if (!detail::getKinematics(candidate.tracks[i], i == 0 ? o2::constants::physics::MassKaonCharged : o2::constants::physics::MassPionCharged, kin[i])) {
       pack.status = BuildStatus::InvalidKinematics;
       return pack;
     }