Remove custom constructors for AudioProcessing::Config.

This CL follows the "Rule of zero".

Those constructors made no sense compared to default generated ones,
since all members are POD.
They were introduced to quiet a memory sanitizer warning,
which apparently was misleading.

As a bonus, the struct is now movable.

Bug: webrtc:11180, webrtc:9855
Change-Id: Iff9fd950bec8040bc6e7e7ece33cc49c5f453f5d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/161381
Reviewed-by: Per Åhgren <peah@webrtc.org>
Commit-Queue: Yves Gerey <yvesg@google.com>
Cr-Commit-Position: refs/heads/master@{#30023}

modules/audio_processing/audio_processing_unittest.cc

@@ -2692,4 +2692,13 @@ TEST(ApmConfiguration, HandlingOfRateCombinations) {
                            capture_channel_counts);
 }
 
+TEST(ApmConfiguration, SelfAssignment) {
+  // At some point memory sanitizer was complaining about self-assigment.
+  // Make sure we don't regress.
+  AudioProcessing::Config config;
+  AudioProcessing::Config* config2 = &config;
+  *config2 = *config2;  // Workaround -Wself-assign-overloaded
+  SUCCEED();  // Real success is absence of defects from asan/msan/ubsan.
+}
+
 }  // namespace webrtc