Revert "gnu: efivar: Update to 36."

This may cause grub-install to fail to update EFI variables, yet complete
with a successful exit code:

Installing for x86_64-efi platform.
Could not prepare Boot variable: No such file or directory.
Installation finished. No error reported.

...causing existing boot entries to disappear.  Investigation pending.

This reverts commit 6e5a6e641a.

gnu/packages/linux.scm

@@ -3939,7 +3939,7 @@ under OpenGL graphics workloads.")
 (define-public efivar
   (package
     (name "efivar")
-    (version "36")
+    (version "35")
     (source (origin
               (method url-fetch)
               (uri (string-append "https://github.com/rhinstaller/" name
@@ -3947,7 +3947,7 @@ under OpenGL graphics workloads.")
                                   "-" version ".tar.bz2"))
               (sha256
                (base32
-                "0cqdikspdmj7imc646q0k7hhw10r8spxa22zm1w0ji49131crgwl"))))
+                "153k2ifyl4giz5fkryxhz8z621diqjy7v25hfga4z94rs32ks0qy"))))
     (build-system gnu-build-system)
     (arguments
      `(;; Tests require a UEFI system and is not detected in the chroot.