Add Unset env feature to deactivate propery

conda.el

@@ -225,7 +225,19 @@ Set for the lifetime of the process.")
             (let ((inhibit-message t))
 	      (message "About to set %s to %s" (car pair) (cdr pair)))
             (setenv (format "%s" (car pair)) (format "%s" (cdr pair))))
-          exports)))
+          exports))
+  (let ((unsets (or (conda-env-params-vars-unset params) '())))
+    (mapc (lambda (arg)
+            (let ((inhibit-message t))
+	      (message "About to unset %s" arg))
+            (setenv (format "%s" arg) ""))
+          unsets))
+ (let ((sets (or (conda-env-params-vars-set params) '())))
+    (mapc (lambda (pair)
+            (let ((inhibit-message t))
+	      (message "About to set %s to %s" (car pair) (cdr pair)))
+            (setenv (format "%s" (car pair)) (format "%s" (cdr pair))))
+          sets)))
 
 (defun conda--set-env-gud-pdb-command-name ()
   "When in a conda environment, call pdb as \\[python -m pdb]."