[pvr] use Refresh() instead of Update() to refresh directory listing

To get rid of the default value for strDirectory in Update() and to gain control of whether we want to clear the cache or not, this will use Refresh() instead of Update() in all PVR windows to refresh the directory listing.
[pvr] cleanup: removes forgotten commented code block
Merge pull request #5031 from xhaggi/pvr-window-refresh

[pvr] use Refresh() instead of Update() to refresh directory listing