Removed arithmetic opcodes with immediate operand

The difference in performance between immediate operands and K operands
does not seem to justify all those extra opcodes. We only keep OP_ADDI,
due to its ubiquity and because the difference is a little more relevant.
(Later, OP_SUBI will be implemented by OP_ADDI, negating the constant.)

ljumptab.h

@@ -45,12 +45,6 @@ static void *disptab[NUM_OPCODES] = {
 &&L_OP_NEWTABLE,
 &&L_OP_SELF,
 &&L_OP_ADDI,
-&&L_OP_SUBI,
-&&L_OP_MULI,
-&&L_OP_MODI,
-&&L_OP_POWI,
-&&L_OP_DIVI,
-&&L_OP_IDIVI,
 &&L_OP_ADDK,
 &&L_OP_SUBK,
 &&L_OP_MULK,