use packaged "opencv" from OS

previously, opencv-2.4.9 was downloaded and compiled from source. now use the precompiled, package version from the OS. this comes in:

Debian Testing (Jessie): 2.4.9
Debian Stable (Wheezy): 2.3.1  # quite old. but is Wheezy still supported? boostrap.sh fails unmodified
Ubuntu 14.04 (Trusty): 2.4.8
Ubuntu 12.04 (Precise): 2.3.1  # not supported anymore?

there are more OS in the osdeps-file, where I just assume they bring similar packaged versions.

tested "image_processing/{frame_helper,stereo} in Jessie and Trusty. but obviously that shouldn't be it. which packages else?

Signed-off-by: Martin Zenzes <martin.zenzes@dfki.de>
remove opencv source-compilation information