Fix packet-pool slot leak in canned message destination picker (#11017)

updateDestinationSelectionList() allocated a MeshPacket via
allocDataPacket() that was never sent or released, permanently
consuming one packetPool slot every time the destination-selection
picker was rebuilt.

On non-PSRAM targets packetPool is a static 70-slot BSS pool, so
repeated picker use exhausts it and eventually blocks all packet
allocation (TX/RX failures). On PSRAM/portduino (MemoryDynamic)
targets it is a true heap leak of ~424B per rebuild.

The allocation and its two field writes (pki_encrypted, channel) were
a copy/paste artifact of the PKI setup in sendText() and had no effect
in this function. Remove the dead allocation.

src/modules/CannedMessageModule.cpp

@@ -289,10 +289,6 @@ void CannedMessageModule::updateDestinationSelectionList()
         }
     }
 
-    meshtastic_MeshPacket *p = allocDataPacket();
-    p->pki_encrypted = true;
-    p->channel = 0;
-
     // Populate active channels
     std::vector<String> seenChannels;
     seenChannels.reserve(channels.getNumChannels());