Removed useless include of qwt header.
Removed useless include of qwt header.

d-tk/dtk,d-tk/dtk,NicolasSchnitzler/dtk,rdebroiz/dtk,d-tk/dtk,d-tk/dtk,NicolasSchnitzler/dtk,rdebroiz/dtk,NicolasSchnitzler/dtk,d-tk/dtk,NicolasSchnitzler/dtk,rdebroiz/dtk,d-tk/dtk,rdebroiz/dtk