Remove unneeded duplicate methods cancel() and isActive()

These can easily be replaced by Loop::cancelTimer() and
Loop::isTimerActive().

This change ensures that timers are now a plain immutable data structure
and offer no methods to change its state.

This also prepares the timer to remove the cyclic dependency with the
loop instance.

Author: clue

src/Timer/Timer.php

@@ -64,20 +64,4 @@ public function isPeriodic()
     {
         return $this->periodic;
     }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function isActive()
-    {
-        return $this->loop->isTimerActive($this);
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function cancel()
-    {
-        $this->loop->cancelTimer($this);
-    }
 }

src/Timer/TimerInterface.php

@@ -33,16 +33,4 @@ public function getCallback();
      * @return bool
      */
     public function isPeriodic();
-
-    /**
-     * Determine whether the time is active
-     *
-     * @return bool
-     */
-    public function isActive();
-
-    /**
-     * Cancel this timer
-     */
-    public function cancel();
 }

tests/Timer/AbstractTimerTest.php

@@ -43,7 +43,7 @@ public function testAddPeriodicTimerWithCancel()
         usleep(1000);
         $this->tickLoop($loop);
 
-        $timer->cancel();
+        $loop->cancelTimer($timer);
 
         usleep(1000);
         $this->tickLoop($loop);
@@ -55,11 +55,11 @@ public function testAddPeriodicTimerCancelsItself()
 
         $loop = $this->createLoop();
 
-        $loop->addPeriodicTimer(0.001, function ($timer) use (&$i) {
+        $loop->addPeriodicTimer(0.001, function ($timer) use (&$i, $loop) {
             $i++;
 
             if ($i == 2) {
-                $timer->cancel();
+                $loop->cancelTimer($timer);
             }
         });
 
@@ -81,7 +81,7 @@ public function testIsTimerActive()
 
         $this->assertTrue($loop->isTimerActive($timer));
 
-        $timer->cancel();
+        $loop->cancelTimer($timer);
 
         $this->assertFalse($loop->isTimerActive($timer));
     }