Remove toString, rely on asString instead when printing stuff

src/main/scala/leon/datagen/VanuatooDataGen.scala

src/main/scala/leon/evaluators/RecursiveEvaluator.scala

src/main/scala/leon/frontends/scalac/CodeExtraction.scala

src/main/scala/leon/frontends/scalac/LeonExtraction.scala

src/main/scala/leon/purescala/CheckADTFieldsTypes.scala

src/main/scala/leon/purescala/Common.scala

src/main/scala/leon/purescala/Types.scala

src/main/scala/leon/repair/rules/Focus.scala

src/main/scala/leon/repair/rules/Split.scala

src/main/scala/leon/solvers/smtlib/SMTLIBSolver.scala

src/main/scala/leon/solvers/z3/AbstractZ3Solver.scala

src/main/scala/leon/synthesis/FileInterface.scala

src/main/scala/leon/synthesis/Problem.scala

src/main/scala/leon/synthesis/Rules.scala

src/main/scala/leon/synthesis/Solution.scala

src/main/scala/leon/synthesis/graph/Graph.scala

src/main/scala/leon/synthesis/graph/Search.scala

src/main/scala/leon/synthesis/rules/ADTDual.scala

src/main/scala/leon/synthesis/rules/ADTInduction.scala

src/main/scala/leon/synthesis/rules/ADTLongInduction.scala