Delete all solvers we're not planning to reimplement anytime soon

src/main/scala/inox/solvers/cvc4/CVC4Solver.scala

src/main/scala/inox/solvers/cvc4/CVC4UnrollingSolver.scala

src/main/scala/inox/solvers/isabelle/AdaptationPhase.scala

src/main/scala/inox/solvers/isabelle/Component.scala

src/main/scala/inox/solvers/isabelle/Functions.scala

...ain/scala/inox/solvers/isabelle/IsabelleEnvironment.scala

src/main/scala/inox/solvers/isabelle/IsabellePhase.scala

src/main/scala/inox/solvers/isabelle/IsabelleSolver.scala

...n/scala/inox/solvers/isabelle/IsabelleSolverFactory.scala

src/main/scala/inox/solvers/isabelle/LeonLoggerFactory.scala

src/main/scala/inox/solvers/isabelle/Translator.scala

src/main/scala/inox/solvers/isabelle/Types.scala

src/main/scala/inox/solvers/isabelle/package.scala

.../inox/solvers/smtlib/SMTLIBCVC4CounterExampleSolver.scala

...ain/scala/inox/solvers/smtlib/SMTLIBCVC4ProofSolver.scala

...cala/inox/solvers/smtlib/SMTLIBCVC4QuantifiedSolver.scala

...cala/inox/solvers/smtlib/SMTLIBCVC4QuantifiedTarget.scala

...in/scala/inox/solvers/smtlib/SMTLIBQuantifiedSolver.scala

...in/scala/inox/solvers/smtlib/SMTLIBQuantifiedTarget.scala

.../scala/inox/solvers/smtlib/SMTLIBZ3QuantifiedSolver.scala