[BOLT] Remove unused MCAnnotation

Author: bgergely0

bolt/include/bolt/Core/MCPlus.h

@@ -72,7 +72,6 @@ class MCAnnotation {
     kLabel,               /// MCSymbol pointing to this instruction.
     kSize,                /// Size of the instruction.
     kDynamicBranch,       /// Jit instruction patched at runtime.
-    kUnkownSign,          /// Signed state not determined yet
     kSigning,             /// Inst is a signing instruction (paciasp, etc.)
     kSigned,              /// Inst is in a range where RA is signed
     kAuthenticating,      /// Authenticating inst (e.g. autiasp)