Remove last_completion_value.

[zherczeg]

Code cleaning, not much effect on performance.

Benchmark	Perf (sec)
3d-cube.js	1.490 -> 1.497 : -0.507%
3d-raytrace.js	1.539 -> 1.551 : -0.763%
access-binary-trees.js	0.763 -> 0.764 : -0.165%
access-fannkuch.js	3.253 -> 3.164 : +2.724%
access-nbody.js	1.589 -> 1.575 : +0.901%
bitops-3bit-bits-in-byte.js	0.793 -> 0.799 : -0.744%
bitops-bits-in-byte.js	1.043 -> 1.050 : -0.681%
bitops-bitwise-and.js	1.945 -> 1.984 : -1.986%
bitops-nsieve-bits.js	2.559 -> 2.530 : +1.154%
controlflow-recursive.js	0.548 -> 0.552 : -0.563%
crypto-aes.js	1.480 -> 1.465 : +0.970%
crypto-md5.js	0.929 -> 0.926 : +0.311%
crypto-sha1.js	0.872 -> 0.871 : +0.109%
date-format-tofte.js	1.173 -> 1.177 : -0.343%
date-format-xparb.js	0.612 -> 0.598 : +2.264%
math-cordic.js	2.000 -> 2.007 : -0.341%
math-partial-sums.js	1.124 -> 1.100 : +2.121%
math-spectral-norm.js	0.888 -> 0.893 : -0.560%
string-base64.js	4.736 -> 4.691 : +0.951%
string-fasta.js	2.267 -> 2.225 : +1.865%
Geometric mean:	+0.343%

[LaszloLango]

This change looks unrelated. Do we really need it in this patch?

[zherczeg]

Removed

[LaszloLango]

@zherczeg, thanks. LGTM

[dbatyai]

LGTM