RISC-V: Remove footnote from the "Zcb" extension

This commit removes excess footnote caused by sloppy copy-and-paste of
other "Zc*" extension lines.

Author: a4lg

crates/std_detect/src/detect/arch/riscv.rs

@@ -69,7 +69,7 @@ features! {
     /// | `"zbkx"`        | Zbkx        | 6.8                |
     /// | `"zbs"`         | Zbs         | 6.5                |
     /// | `"zca"`         | Zca         | 6.11 [^dep]        |
-    /// | `"zcb"`         | Zcb         | 6.11 [^dep]        |
+    /// | `"zcb"`         | Zcb         | 6.11               |
     /// | `"zcd"`         | Zcd         | 6.11 [^dep]        |
     /// | `"zcf"`         | Zcf         | 6.11 [^dep]        |
     /// | `"zcmop"`       | Zcmop       | 6.11               |