Optional: Use nullopt and implicit construction in /pc/peerconnectionendtoend_unittest.cc

Changes places where we explicitly construct an Optional to instead use
nullopt or the requisite value type only.

This CL was uploaded by git cl split.

R=hbos@webrtc.org

Bug: None
Change-Id: I2fc923e788b744fc167f02f9fecd19bea512af81
Reviewed-on: https://webrtc-review.googlesource.com/23613
Commit-Queue: Oskar Sundbom <ossu@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20834}
diff --git a/pc/peerconnectionendtoend_unittest.cc b/pc/peerconnectionendtoend_unittest.cc
index 8b16610..17f48bf 100644
--- a/pc/peerconnectionendtoend_unittest.cc
+++ b/pc/peerconnectionendtoend_unittest.cc
@@ -277,7 +277,7 @@
       format.name = "L16";
       return webrtc::AudioEncoderL16::SdpToConfig(format);
     } else {
-      return rtc::Optional<Config>();
+      return rtc::nullopt;
     }
   }
   static void AppendSupportedEncoders(
@@ -312,7 +312,7 @@
       format.name = "L16";
       return webrtc::AudioDecoderL16::SdpToConfig(format);
     } else {
-      return rtc::Optional<Config>();
+      return rtc::nullopt;
     }
   }
   static void AppendSupportedDecoders(