Fix return type in phpdoc annotations

Author: Art4

src/Redmine/Api/Attachment.php

@@ -98,7 +98,7 @@ public function upload($attachment, $params = [])
      *
      * @param int $id id of the attachment
      *
-     * @return false|SimpleXMLElement|string
+     * @return string empty string on success
      */
     public function remove($id)
     {

src/Redmine/Api/Group.php

@@ -203,7 +203,7 @@ public function show($id, array $params = [])
      *
      * @param int $id id of the group
      *
-     * @return string
+     * @return string empty string on success
      */
     public function remove($id)
     {
@@ -250,7 +250,7 @@ public function addUser($id, $userId)
      * @param int $id     id of the group
      * @param int $userId id of the user
      *
-     * @return string
+     * @return string empty string on success
      */
     public function removeUser($id, $userId)
     {

src/Redmine/Api/Issue.php

@@ -296,7 +296,7 @@ public function addWatcher($id, $watcherUserId)
      * @param int $id
      * @param int $watcherUserId
      *
-     * @return false|SimpleXMLElement|string
+     * @return string empty string on success
      */
     public function removeWatcher($id, $watcherUserId)
     {
@@ -439,7 +439,7 @@ public function attachMany($id, array $attachments)
      *
      * @param int $id the issue number
      *
-     * @return false|SimpleXMLElement|string
+     * @return string empty string on success
      */
     public function remove($id)
     {

src/Redmine/Api/IssueCategory.php

@@ -230,7 +230,7 @@ public function update($id, array $params)
      * @param int   $id     id of the category
      * @param array $params extra GET parameters
      *
-     * @return string
+     * @return string empty string on success
      */
     public function remove($id, array $params = [])
     {

src/Redmine/Api/IssueRelation.php

@@ -118,7 +118,7 @@ public function show($id)
      *
      * @param int $id the relation id
      *
-     * @return string
+     * @return string empty string on success
      */
     public function remove($id)
     {

src/Redmine/Api/Membership.php

@@ -163,7 +163,7 @@ public function update($id, array $params = [])
      *
      * @param int $id id of the membership
      *
-     * @return false|\SimpleXMLElement|string
+     * @return string empty string on success
      */
     public function remove($id)
     {

src/Redmine/Api/Project.php

@@ -392,7 +392,7 @@ protected function prepareParamsXml($params)
      *
      * @param int $id id of the project
      *
-     * @return false|\SimpleXMLElement|string
+     * @return string empty string on success
      */
     public function remove($id)
     {

src/Redmine/Api/TimeEntry.php

@@ -187,7 +187,7 @@ public function update($id, array $params)
      *
      * @param int $id id of the time entry
      *
-     * @return false|\SimpleXMLElement|string
+     * @return string empty string on success
      */
     public function remove($id)
     {

src/Redmine/Api/User.php

@@ -263,7 +263,7 @@ public function update($id, array $params)
      *
      * @param int $id id of the user
      *
-     * @return false|\SimpleXMLElement|string
+     * @return string empty string on success
      */
     public function remove($id)
     {

src/Redmine/Api/Version.php

@@ -266,7 +266,7 @@ private function validateSharing(array $params = [])
      *
      * @param int $id id of the version
      *
-     * @return string
+     * @return string empty string on success
      */
     public function remove($id)
     {