Exception handling for endpointFocus causes a different type of Excep…

…tion to be thrown for the focus. In my opinion, it is better to throw Java.lang.IllegalArgumentException for all those 3 cases:

1. endpointFocus does not exist
2. endpointPrefix does not exist
3. Both endpointFocus and endpointPrefix are provided.

core/src/main/kotlin/org/evomaster/core/problem/rest/EndpointFilter.kt

@@ -15,12 +15,6 @@ object EndpointFilter {
         val all = swagger.paths.map{it.key}
 
         val selection =  if(config.endpointFocus != null) {
-            if (all.none { it == config.endpointFocus }) {
-                throw IllegalArgumentException(
-                    "Invalid endpointFocus: ${config.endpointFocus}. " +
-                            "\nAvailable:\n${all.joinToString("\n")}"
-                )
-            }
             all.filter { it != config.endpointFocus }
         } else if(config.endpointPrefix != null){
             all.filter { ! it.startsWith(config.endpointPrefix!!) }