Delete code not needed by InstallPlan.
Delete code not needed by InstallPlan.

Critically, InstallPlan no longer levies solver-style sanity checks
(e.g., whether or not the packages are consistent); it's assumed
the SolverInstallPlan checks this, and that processing an InstallPlan
is unlikely to cause problems here.

Signed-off-by: Edward Z. Yang <dbd597f5635f432486c5d365e9bb585b3eaa1853@cs.stanford.edu>

sopvop/cabal,mydaum/cabal,kolmodin/cabal,themoritz/cabal,themoritz/cabal,mydaum/cabal,sopvop/cabal,themoritz/cabal,kolmodin/cabal,sopvop/cabal