Revert "build-self: Let HOME pass through the execution environment."

This reverts commit 48d498c2.
It breaks ‘guix pull’.

build-aux/build-self.scm

@@ -399,7 +399,6 @@ (define* (build source
   (mlet %store-monad ((build  (build-program source version guile-version
                                              #:pull-version pull-version))
                       (system (if system (return system) (current-system)))
-                      (home   (getenv "HOME"))
 
                       ;; Note: Use the deprecated names here because the
                       ;; caller might be Guix <= 0.16.0.
@@ -420,9 +419,6 @@ (define* (build source
                          ;; $GUILE_LOAD_PATH & co.
                          (with-clean-environment
                           (setenv "GUILE_WARN_DEPRECATED" "no") ;be quiet and drive
-                          (when home
-                            ;; Inherit HOME so that 'xdg-directory' works.
-                            (setenv "HOME" home))
                           (open-pipe* OPEN_READ
                                       (derivation->output-path build)
                                       source system version