iOS: Include legacy objc API in all.gyp + fix H264 libyuv dependency

The legacy objc API is not included in the GYP generation if include_tests=0.
This causes problems downstream in some cases, so it's changed in this CL.

The libyuv dependency needs to be possible to disable using the build_libyuv
GYP variable.

NOTRY=True

Review URL: https://codereview.webrtc.org/1705733002

Cr-Commit-Position: refs/heads/master@{#11652}

webrtc/modules/video_coding/codecs/h264/h264.gypi

@@ -62,9 +62,6 @@
         {
           'target_name': 'webrtc_h264_video_toolbox',
           'type': 'static_library',
-          'dependencies': [
-            '<(DEPTH)/third_party/libyuv/libyuv.gyp:libyuv',
-          ],
           'link_settings': {
             'xcode_settings': {
               'OTHER_LDFLAGS': [
@@ -83,6 +80,11 @@
             'h264_video_toolbox_nalu.cc',
             'h264_video_toolbox_nalu.h',
           ],
+          'conditions': [
+            ['build_libyuv==1', {
+              'dependencies': ['<(DEPTH)/third_party/libyuv/libyuv.gyp:libyuv'],
+            }],
+          ],
         }, # webrtc_h264_video_toolbox
       ], # targets
     }], # OS=="ios"