opencv: Remove blacklist

Opencv 3.1 builds fine with ffmpeg.

ricardo@neopili:~/curro/qt5022/oe/openembedded-core/build$ bitbake
opencv
Loading cache: 100%
|############################################################################|
ETA:  00:00:00
Loaded 2018 entries from dependency cache.
NOTE: Resolving any missing task queue dependencies

Build Configuration:
BB_VERSION        = "1.29.0"
BUILD_SYS         = "x86_64-linux"
NATIVELSBSTRING   = "Debian-testing"
TARGET_SYS        = "i586-oe-linux"
MACHINE           = "qemux86"
DISTRO            = "nodistro"
DISTRO_VERSION    = "nodistro.0"
TUNE_FEATURES     = "m32 i586"
TARGET_FPU        = ""
meta              = "master:300f858ba07c938427ccd05a3d7220027a03d461"
meta-oe           = "master:29462f7161b346dbc2ea00830da869a0a1c35fb9"

NOTE: Preparing RunQueue
NOTE: Executing SetScene Tasks
NOTE: Executing RunQueue Tasks
NOTE: Tasks Summary: Attempted 1242 tasks of which 1228 didn't need to
be rerun and all succeeded.

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>