media: staging/intel-ipu3: remove TODO item about acronyms

The Imgu acronyms are moved from header file into Document by previous
commit b8726aea

 ("media: ipu3: update meta format documentation"), so
the item can be removed from TODO list now.

[Sakari Ailus: Use commit [0-9a-f]{12} plus subject]

Signed-off-by: Bingbu Cao <bingbu.cao@intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>