Rewinds the descriptor's next-index counter by one.
Declared in <wallet/scriptpubkeyman.h>
[[requires_capability(0x7ff371803978), requires_capability(0x7ff365630dd8), requires_capability(0x7ff35d350958), requires_capability(0x7ff365aaa8c8), requires_capability(0x7ff379b45cd8), requires_capability(0x7ff37e1e2388)]]
void
DecIndex();