In cases, when already non-prototypes items are added to a graph prototype (discovered by nested LLD), and LLD rule is no longer discovered and removed - the graphs are not deleted. 

Steps to reproduce:

1. Import the host: host-graph-issue.yaml
2. Start Zabbix server
3. Execute the discovery rule "TEST" on the imported host for several times, to discover all the entities
4. Observe that graphs are created, and contains the discovered item, and host's trapper item "trap"
5. Change the status Discover -> No for LLD prototype: "Discover tablespaces for {#DB}"
6. Execute the LLD "TEST"
7. Open graphs

Result:
The graphs, that were created by Nested LLD, are still present. (Displayed with empty discovered by field and error in the php log.)

Error in php log:

Undefined array key "discoveryRulePrototype" [zabbix.php:17 -> require_once() -> ZBase->run() -> ZBase->processRequest() -> ZBase->processResponseFinal() -> CView->getOutput() -> include() -> CTabView->addTab() -> CDiv->__construct() -> CTag->addItem() -> CObject->addItem() -> unpack_object() -> CPartial->getOutput() -> include() -> CConfigFile->{closure}() in app/partials/graph.edit.graph.tab.php:34]
Trying to access array offset on value of type null [zabbix.php:17 -> require_once() -> ZBase->run() -> ZBase->processRequest() -> ZBase->processResponseFinal() -> CView->getOutput() -> include() -> CTabView->addTab() -> CDiv->__construct() -> CTag->addItem() -> CObject->addItem() -> unpack_object() -> CPartial->getOutput() -> include() -> CConfigFile->{closure}() in app/partials/graph.edit.graph.tab.php:39]

Expected:
Probably in such case, graphs related to non-existing nested LLD should be removed.