SearchContext should not hold duplicate information

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

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

src/main/scala/leon/synthesis/SearchContext.scala

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

...st/scala/leon/integration/solvers/StringRenderSuite.scala

...scala/leon/regression/synthesis/StablePrintingSuite.scala