ncm-mkgridmap: fix incorrect argument passed to CAF::Process

Blocking issue for 14.10.0 release (https://github.com/quattor/release/issues/58) due to lack of testing in previous modification (#49). My fault!
You don't need this function. `LC::Process` will internally split the command for you, if you just pass it a single string. Just do:

```perl
my $proc = CAF::Process->new([$entry->{command}], log => $self);
``` 

and the right thing will happen.