Remove cache prefetch code.

Remove cache prefetch code.

The performance is decreased with cache prefetch, especially for
ATOM. So remove these code. Following is the experiment.

old: 0.19.5-with-cache-prefetch
new: 0.19.5-without-cache-prefetch

CPU: Intel Atom N270@1.6GHz
OS: MeeGo (32 bits)
Speedups
========
image-rgba                    poppler-0    17125.68 (17279.58 0.92%) -> 14765.36 (15926.49 3.54%):  1.16x speedup
image-rgba                  ocitysmap-0    9008.25 (9040.41 7.50%) -> 8277.94 (8343.09 5.44%):  1.09x speedup
image-rgba          xfce4-terminal-a1-0    18020.76 (18230.68 0.97%) -> 16703.77 (16712.42 1.22%):  1.08x speedup
image-rgba         gnome-terminal-vim-0    25081.38 (25133.38 0.24%) -> 23407.47 (23652.98 0.54%):  1.07x speedup
image-rgba          firefox-talos-gfx-0    57916.97 (57973.20 0.11%) -> 54556.64 (54624.55 0.39%):  1.06x speedup
image-rgba       firefox-planet-gnome-0    102377.47 (103496.63 0.70%) -> 96816.65 (97075.54 0.15%):  1.06x speedup
image-rgba         swfdec-giant-steps-0    12376.24 (12616.84 1.02%) -> 11705.30 (11825.20 1.06%):  1.06x speedup

CPU: Intel Core(TM)2 Duo CPU T9600@2.80GHz
OS: Ubuntu 10.04 (64bits)
Speedups
========
image-rgba                  ocitysmap-0    2671.46 (2691.82 8.55%) -> 2296.20 (2307.26 5.77%):  1.16x speedup
image-rgba         swfdec-giant-steps-0    1614.55 (1615.18 1.68%) -> 1532.84 (1538.52 0.72%):  1.05x speedup

Signed-off-by: Liu Xinyun <xinyun.liu@intel.com>
Signed-off-by: Chen Miaobo <miaobo.chen@intel.com>