Serve EPUBs instead XTC in daily OPDS

It turns out it is currently impossible for the Xteink X4 to download
XTC files from an OPDS server. So I switched the built-in OPDS server in
this binary (daily.hallada.net/opds) to serve the EPUB files instead of
the XTC files. The X4 is pretty capable of reading the X4 edition of the
EPUB that was optimized for it anyways, and I prefer the flexibility of
EPUB, so I might end up eventually deleting the XTC conversion. For now,
I kept the conversion step (in case I ever want to ever try manually
copying them to the device) and I keep a limited number of XTC issues on
the server since they are quite big in filesize. The BookOrbit
integration is now optional since the built-in OPDS server is able to
serve the EPUBs. In my installation, I serve the EPUBs through both. The
daily.hallada.net/opds server is just a little quicker to navigate and
download the EPUBs on the X4 since the BookOrbit OPDS requires diving
into a couple layers of folders before you get to the files.

src/main.rs

@@ -31,7 +31,7 @@ struct Cli {
 enum Command {
     /// Build (and publish) one issue.
     Generate(GenerateArgs),
-    /// Run the rating endpoints, XTC OPDS feed and static files.
+    /// Run the rating endpoints, the OPDS catalog and downloads.
     Serve,
     /// Taste-profile maintenance.
     #[command(subcommand)]
@@ -167,9 +167,6 @@ fn print_outcome(outcome: &GenerateOutcome) {
             if let Some(xtc) = &published.xtc {
                 println!("published: {}", xtc.display());
             }
-            if let Some(opds) = &published.opds {
-                println!("opds:      {}", opds.display());
-            }
             if published.pruned > 0 {
                 println!("pruned:    {} expired files", published.pruned);
             }