Some updates of decfiles for powheg generation

Remove the two processes that are not supported by Powheg now,

• incl_b,powheg.dec
• incl_c,powheg.dec

Migrate the 10 processes that use Powheg as generator to new format,

• Higgs_ZZ_eeee.dec
• Higgs_ZZ_mumuee.dec
• Higgs_ZZ_mumumumu.dec
• Wbb_lnul,bb=1l,5Gev,2b,powheg.dec
• ZZ_eeee.dec
• ZZ_mumuee.dec
• ZZ_mumumumu.dec
• Z_ee_PowHeg40GeV.dec
• Z_mumu_PowHeg40GeV.dec
• tt_bb=1l,10GeV,2b,powheg.dec