tests: utils: Don't calculate file size in virTestLoadFile
tests: utils: Don't calculate file size in virTestLoadFile

The callers don't use it so don't waste a strlen(). Also fix the comment
for the function.

Reviewed-by: Eric Blake <a9da18479c871fe903d9590822cfe2629c6a4d11@redhat.com>

fabianfreyer/libvirt,andreabolognani/libvirt,jfehlig/libvirt,crobinso/libvirt,zippy2/libvirt,fabianfreyer/libvirt,eskultety/libvirt,datto/libvirt,jardasgit/libvirt,crobinso/libvirt,olafhering/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,eskultety/libvirt,crobinso/libvirt,datto/libvirt,jardasgit/libvirt,eskultety/libvirt,datto/libvirt,datto/libvirt,datto/libvirt,zippy2/libvirt,nertpinx/libvirt,libvirt/libvirt,fabianfreyer/libvirt,crobinso/libvirt,libvirt/libvirt,libvirt/libvirt,libvirt/libvirt,nertpinx/libvirt,andreabolognani/libvirt,jardasgit/libvirt,eskultety/libvirt,zippy2/libvirt,olafhering/libvirt,jfehlig/libvirt,jfehlig/libvirt,eskultety/libvirt,jardasgit/libvirt,zippy2/libvirt,nertpinx/libvirt,andreabolognani/libvirt,nertpinx/libvirt,jardasgit/libvirt,olafhering/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,olafhering/libvirt