profiles: Really disable deprecation warnings for 'profile-derivation'.

This is a followup to 2815fca142.

* guix/profiles.scm (profile-derivation)[builder]: Remove
'debug-disable' call, which was ineffective.
Pass #:env-vars to 'gexp->derivation'.

guix/profiles.scm

@@ -1268,9 +1268,6 @@ are cross-built for TARGET."
                          (guix search-paths)
                          (srfi srfi-1))
 
-            ;; Don't complain about _IO* on Guile 2.2.
-            (debug-disable 'warn-deprecated)
-
             (setvbuf (current-output-port) _IOLBF)
             (setvbuf (current-error-port) _IOLBF)
 
@@ -1293,6 +1290,9 @@ are cross-built for TARGET."
                       #:system system
                       #:target target
 
+                      ;; Don't complain about _IO* on Guile 2.2.
+                      #:env-vars '(("GUILE_WARN_DEPRECATED" . "no"))
+
                       ;; Not worth offloading.
                       #:local-build? #t