x86emul: prune an excess EVEX.Z check

DstMem processing early in x86_emulate() raises #UD when EVEX.Z is set
with a memory destination. Open-coded checks like this one are therefore
dead / unreachable code, violating Misra rules.

Fixes: 4037a62ef9 ("x86emul: support AVX512F floating-point conversion insns")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/x86_emulate/x86_emulate.c

@@ -7350,7 +7350,7 @@ x86_emulate(
         if ( evex_encoded() )
         {
             generate_exception_if((evex.w || evex.reg != 0xf || !evex.RX ||
-                                   (ea.type != OP_REG && (evex.z || evex.brs))),
+                                   (ea.type != OP_REG && evex.brs)),
                                   X86_EXC_UD);
             host_and_vcpu_must_have(avx512f);
             avx512_vlen_check(false);