search: Don't strip .desktop suffix overzealously

This commit changes the search command to properly output the app ID for
IDs that end in .desktop, e.g. to print org.telegram.desktop rather than
org.telegram.

Fixes https://github.com/flatpak/flatpak/issues/4535

(cherry picked from commit 62e09b406b8a7fb517c294d2c0b149a83f2cc64b)