leave() and leave_group() inconsitencies in return values

[andres.fortier]

From ElggGroup.php:

/**
 * Remove a user from a group.
 *
 * @param int $group_guid The group.
 * @param int $user_guid  The user.
 *
 * @return bool
 */
function leave_group($group_guid, $user_guid)

On success it returns 1, not true. And then:

/**
 * Remove a user from the group.
 *
 * @param ElggUser $user User
 *
 * @return void
 */
public function leave(ElggUser $user)
{
return leave_group($this->getGUID(), $user->getGUID());
}

Thus, the function states it returns void while it really returns a number representing a boolean.

[cash]

Fixes #4118 returning bool from leave group functions

Changeset: 30630b3a25e37430d966af6e6af933b7d000ab1a

[cash]

Fixes #4118 returning bool from leave group functions

Changeset: 90baebb659b3e47dac24da969e232ff0cef94a1b