Revert "new visitors FunctionTypeFinder,UnionBasisChecker"

This reverts commit 29caaa1e8de57a2c4e4ad2c2d90d1e088dedb24a.

Conflicts:
	core/typechecker/src/main/java/org/overture/typechecker/assistant/ITypeCheckerAssistantFactory.java
	core/typechecker/src/main/java/org/overture/typechecker/assistant/TypeCheckerAssistantFactory.java
	core/typechecker/src/main/java/org/overture/typechecker/assistant/type/ANamedInvariantTypeAssistantTC.java
	core/typechecker/src/main/java/org/overture/typechecker/visitor/TypeCheckerExpVisitor.java
	core/typechecker/src/main/java/org/overture/typechecker/visitor/TypeCheckerOthersVisitor.java