[FL-2868] Remove string_push_uint64 (#1832)

* Remove string_pust_uint64
* Oops, furi strings now
* Remove dead code
* Remove unneeded import

Co-authored-by: あく <alleteam@gmail.com>

lib/nfc/parsers/plantain_parser.h

@@ -8,6 +8,4 @@ bool plantain_parser_read(NfcWorker* nfc_worker, FuriHalNfcTxRxContext* tx_rx);
 
 bool plantain_parser_parse(NfcDeviceData* dev_data);
 
-void string_push_uint64(uint64_t input, FuriString* output);
-
 uint8_t plantain_calculate_luhn(uint64_t number);