Prune old installers from the remote feed on push

rsync without --delete left every previous version on the server (the
screenshot showed 0.1.0 and 0.1.1 side by side). The push now removes
non-current installers over ssh first, so the remote feed mirrors the local
one whether the transfer uses rsync or tar.

deploy/push_desktop.sh

@@ -92,6 +92,16 @@ if [ -n "$REMOTE" ]; then
 
     echo
     echo "==> Copying the feed to $REMOTE_TARGET:$REMOTE_FEED ..."
+    if ! ssh "$REMOTE_TARGET" "mkdir -p '$REMOTE_FEED'"; then
+        echo "ssh to $REMOTE_TARGET failed; nothing was copied." >&2
+        exit 1
+    fi
+    # The remote feed keeps only the current version, like the local one.
+    if ! ssh "$REMOTE_TARGET" \
+        "find '$REMOTE_FEED' -maxdepth 1 -type f \\( -name '*.deb' -o -name '*.pkg.tar.zst' -o -name '*.exe' -o -name '*.exe.blockmap' \\) ! -name '*$VERSION*' -exec rm -f {} +"; then
+        echo "==> Could not prune old installers on $REMOTE_TARGET (continuing)." >&2
+    fi
+
     transferred=0
     if command -v rsync >/dev/null 2>&1; then
         if rsync -a --info=progress2 "$FEED"/ "$REMOTE_TARGET:$REMOTE_FEED/"; then
@@ -101,10 +111,6 @@ if [ -n "$REMOTE" ]; then
         fi
     fi
     if [ "$transferred" -eq 0 ]; then
-        if ! ssh "$REMOTE_TARGET" "mkdir -p '$REMOTE_FEED'"; then
-            echo "ssh to $REMOTE_TARGET failed; nothing was copied." >&2
-            exit 1
-        fi
         if ! tar -C "$FEED" -cf - . |
             ssh "$REMOTE_TARGET" "tar -C '$REMOTE_FEED' -xf -"; then
             echo "Copy to $REMOTE_TARGET:$REMOTE_FEED failed." >&2