cmTarget: Remove dead code.

Whitelisting of properties already ensures that the LOCATION
property will not be read from an INTERFACE_LIBRARY.

Source/cmTarget.cxx

@@ -2688,7 +2688,6 @@ const char *cmTarget::GetProperty(const char* prop,
      this->GetType() == cmTarget::STATIC_LIBRARY ||
      this->GetType() == cmTarget::SHARED_LIBRARY ||
      this->GetType() == cmTarget::MODULE_LIBRARY ||
-     this->GetType() == cmTarget::INTERFACE_LIBRARY ||
      this->GetType() == cmTarget::UNKNOWN_LIBRARY)
     {
     if(strcmp(prop,"LOCATION") == 0)