Remove three checked GitLabApiException (gitlab4j#928)

There was not chance of throwing checked exception GitLabApiException  from given three methods. I have removed them to make user code using given methods easier to read.

src/main/java/org/gitlab4j/api/Pager.java

@@ -255,9 +255,8 @@ public void remove() {
      * Returns the first page of List. Will rewind the iterator.
      *
      * @return the first page of List
-     * @throws GitLabApiException if any error occurs
      */
-    public List<T> first() throws GitLabApiException {
+    public List<T> first() {
         return (page(1));
     }
 
@@ -280,19 +279,17 @@ public List<T> last() throws GitLabApiException {
      * Returns the previous page of List. Will set the iterator to the previous page.
      *
      * @return the previous page of List
-     * @throws GitLabApiException if any error occurs
      */
-    public List<T> previous() throws GitLabApiException {
+    public List<T> previous() {
         return (page(currentPage - 1));
     }
 
     /**
      * Returns the current page of List.
      *
      * @return the current page of List
-     * @throws GitLabApiException if any error occurs
      */
-    public List<T> current() throws GitLabApiException {
+    public List<T> current() {
         return (page(currentPage));
     }