Crosscorr cleanup (#14936)

* Simplify code for convolution destination type/size

For the 2d filter code, destination size equals source size, and the
crossCorr function even (re-)creates the output matrix with the given size.

The number of channels also have to match. The destination type() is the
one used to create the output matrix, so we can use its type() here.

This is a preparatory patch.
Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>

* Remove redundant destination size and type parameters from crossCorr

All calling sites of crossCorr already use (...,
mat, mat.size(), mat.type(), ...), so the parameters are redundant.
Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>