[xcc,sim] Eliminated slori instruction

the "li" macro in RISC-V assembly isn't as efficient anymore for 64b
constants, and "la" doesn't work for 64b addresses with ".set noat".
But it's worth it to remove an ugly instruction.

riscv/execute.h

@@ -336,11 +336,6 @@ switch((insn.bits >> 0x19) & 0x7f)
     #include "insns/lui.h"
     break;
   }
-  case 0x72:
-  {
-    #include "insns/slori.h"
-    break;
-  }
   case 0x73:
   {
     switch((insn.bits >> 0xc) & 0x7)