Don't reference even more non-existant usb string descriptors

teensy3/usb_desc.c

         0x06,                                   // bInterfaceClass (0x06 = still image)
         0x01,                                   // bInterfaceSubClass
         0x01,                                   // bInterfaceProtocol
-        4,                                      // iInterface
+        0,                                      // iInterface
         // endpoint descriptor, USB spec 9.6.6, page 269-271, Table 9-13
         7,                                      // bLength
         5,                                      // bDescriptorType

teensy4/usb_desc.c

         0x06,                                   // bInterfaceClass (0x06 = still image)
         0x01,                                   // bInterfaceSubClass
         0x01,                                   // bInterfaceProtocol
-        4,                                      // iInterface
+        0,                                      // iInterface
         // endpoint descriptor, USB spec 9.6.6, page 269-271, Table 9-13
         7,                                      // bLength
         5,                                      // bDescriptorType
         0x06,                                   // bInterfaceClass (0x06 = still image)
         0x01,                                   // bInterfaceSubClass
         0x01,                                   // bInterfaceProtocol
-        4,                                      // iInterface
+        0,                                      // iInterface
         // endpoint descriptor, USB spec 9.6.6, page 269-271, Table 9-13
         7,                                      // bLength
         5,                                      // bDescriptorType