environment: Remove deprecated -E/--exec option.

* guix/scripts/environment.scm (%options): Remove "--exec", which was
deprecated in commit 1de2fe95e0 in 2015.
* tests/guix-environment.sh: Remove use of '-E'.

guix/scripts/environment.scm

@@ -220,9 +220,6 @@ COMMAND or an interactive shell in that environment.\n"))
                    (alist-cons 'inherit-regexp
                                (make-regexp* arg)
                                result)))
-         (option '(#\E "exec") #t #f ; deprecated
-                 (lambda (opt name arg result)
-                   (alist-cons 'exec (list %default-shell "-c" arg) result)))
          (option '("search-paths") #f #f
                  (lambda (opt name arg result)
                    (alist-cons 'search-paths #t result)))

tests/guix-environment.sh

@@ -117,16 +117,6 @@ case "`uname -m`" in
 	;;
 esac
 
-
-# Same as above, but with deprecated -E flag.
-if guix environment --bootstrap --ad-hoc guile-bootstrap --pure \
-        -E "guile -c '(exit 42)'"
-then
-    false
-else
-    test $? = 42
-fi
-
 # Make sure we can build the environment of 'guix'.  There may be collisions
 # in its profile (e.g., for 'gzip'), but we have to accept them.
 guix environment guix --bootstrap -n