Filter Wizard: use more apt variable names

Signed-off-by: Tim Harder <timothy.harder@analog.com>
Filter Wizard: remove unnecessary whitespace

Signed-off-by: Tim Harder <timothy.harder@analog.com>
Filter Wizard: remove unused functions

They're probably from old versions of the file that was exported when
building the user interface with guide.

Signed-off-by: Tim Harder <timothy.harder@analog.com>