Removed bytecode transformation for sequence packing/unpacking.

It depended on the previously removed basic block checker to
prevent a jump into the middle of the transformed block.

Clears SF 757818: tuple assignment -- SystemError: unknown opcode

Python/compile.c

@@ -363,34 +363,6 @@ optimize_code(PyObject *code, PyObject* consts)
 			SETARG(codestr, i, 4);
 			break;
 
-		/* Replace BUILD_SEQN 2 UNPACK_SEQN 2 with ROT2 JMP+2.
-		   Replace BUILD_SEQN 3 UNPACK_SEQN 3 with ROT3 ROT2 JMP+1.
-		   Note, these opcodes occur together only in assignment
-		   statements.  Accordingly, the unpack opcode is never
-		   a jump target.  */
-		case BUILD_TUPLE:
-		case BUILD_LIST:
-			if (codestr[i+3] != UNPACK_SEQUENCE)
-				continue;
-			if (GETARG(codestr, i) == 2 && \
-			    GETARG(codestr, i+3) == 2) {
-				codestr[i] = ROT_TWO;
-				codestr[i+1] = JUMP_FORWARD;
-				SETARG(codestr, i+1, 2);
-				codestr[i+4] = DUP_TOP;	 /* Filler codes used as NOPs */
-				codestr[i+5] = POP_TOP;
-				continue;
-			} 
-			if (GETARG(codestr, i) == 3 && \
-			    GETARG(codestr, i+3) == 3) {
-				codestr[i] = ROT_THREE;
-				codestr[i+1] = ROT_TWO;
-				codestr[i+2] = JUMP_FORWARD;
-				SETARG(codestr, i+2, 1);	
-				codestr[i+5] = DUP_TOP;
-			}
-			break;
-
 		/* Replace jumps to unconditional jumps */
 		case FOR_ITER:
 		case JUMP_FORWARD: