Fix Tor Browser being called "Tails documentation" in the top bar (refs: #15101).

Fix against 14d5feb3.

Now that there were multiple .desktop files that claim the "Tor Browser"
WM_CLASS, GNOME got confused and picked the wrong one. Apparently giving
tor-browser.desktop its own StartupWMClass is enough to fix that.

config/chroot_local-includes/etc/skel/Desktop/Report_an_error.desktop.in

@@ -7,4 +7,3 @@ Terminal=false
 Exec=/usr/local/bin/tails-documentation support
 Icon=/usr/share/pixmaps/whisperback.svg
 StartupNotify=true
-StartupWMClass=Tor Browser

config/chroot_local-includes/etc/skel/Desktop/tails-documentation.desktop.in

@@ -7,4 +7,3 @@ Terminal=false
 Exec=/usr/local/bin/tails-documentation doc
 Icon=/usr/share/icons/gnome/48x48/categories/system-help.png
 StartupNotify=true
-StartupWMClass=Tor Browser

config/chroot_local-includes/usr/share/applications/tails-documentation.desktop.in

@@ -9,4 +9,3 @@ Terminal=false
 Exec=/usr/local/bin/tails-documentation doc
 Icon=/usr/share/icons/gnome/48x48/categories/system-help.png
 StartupNotify=true
-StartupWMClass=Tor Browser

config/chroot_local-includes/usr/share/applications/tor-browser.desktop.in

@@ -8,3 +8,4 @@ Terminal=false
 Type=Application
 Exec=/usr/local/bin/tor-browser %u
 StartupNotify=true
+StartupWMClass=Tor Browser