gnu: fuse@3: Bind to default FUSE variable.

* gnu/packages/linux.scm (fuse): Rename this…
(fuse-2): …to this, and…
(fuse-3): …rename this…
(fuse): …to this!
(fuse-static): Rename this…
(fuse-2-static): …to this.
Adjust all users.

gnu/packages/bootloaders.scm

@@ -215,8 +215,8 @@
        ;; file system will be readable by GRUB without rebooting.
        ,@(if (member (or (%current-target-system)
                          (%current-system))
-                     (package-supported-systems fuse))
-             `(("fuse" ,fuse))
+                     (package-supported-systems fuse-2))
+             `(("fuse" ,fuse-2))
              '())
 
        ("freetype" ,freetype)