[RISCV] Remove feature implication from Zvknhb.

We don't have feature implications on any other Zvk extensions and
we have error messages in RISCVISAInfo if Zve or V is not enabled.
I'm working on testing and refactoring in that code so I'd like to
make it consistent.

llvm/lib/Target/RISCV/RISCVFeatures.td

@@ -780,8 +780,7 @@ def HasStdExtZvknha : Predicate<"Subtarget->hasStdExtZvknha()">,
 
 def FeatureStdExtZvknhb
     : RISCVExtension<"zvknhb", 1, 0,
-                     "'Zvknhb' (Vector SHA-2 (SHA-256 and SHA-512))",
-                     [FeatureStdExtZve64x]>,
+                     "'Zvknhb' (Vector SHA-2 (SHA-256 and SHA-512))">,
       RISCVExtensionBitmask<0, 56>;
 def HasStdExtZvknhb : Predicate<"Subtarget->hasStdExtZvknhb()">,
                       AssemblerPredicate<(all_of FeatureStdExtZvknhb),