Removes the environment variable variable from the provided environment envp.
| envp | 
                 an environment list that can be freed using strfreev (e.g., as returned from @get), or null for an empty environment list  | 
            
| variable | 
                 the environment variable to remove, must not contain '='  | 
            
| 
                 the updated environment list. Free it using strfreev.  |