With previous patch, we accept negative value as length of string to
duplicate. So there is no need to pass strlen(src) in case we want to do
duplicate the whole string.
The source code base needs to be adapted as well. Some files
include virutil.h just for the string related functions (here,
the include is substituted to match the new file), some include
virutil.h without any need (here, the include is removed), and
some require both.
