Removed LEGACY_BITEXACT from neteq_impl.cc and updated the ACM unit tests.

I'll be rewriting AcmReceiver soon and am trying to reduce the amount of
old stuff that needs to be supported.

I've manually checked the outputs of the AcmReceiver bitexactness
tests with this change. A large part of the tests are still bitexact,
with one section only differing slightly in timings. Nothing audible
unless playing the old and new versions back simultaneously.

The output of NetEqDecoderTest were also changed due to this CL, although only on android. I built and ran the test locally and compared the audio output manually - the changes were the same as for the other tests; i.e. very slight timing changes for a part of the output.

I updated the network stats checksum for android without analyzing it further. I expect it goes hand-in-hand with the changes to the output; i.e. the changes in it are fine because the audio output is fine. Likely, the stats will show changes in the usage of CNG, since that is what the code changes.

BUG=webrtc:1361

Review-Url: https://codereview.webrtc.org/2117763002
Cr-Commit-Position: refs/heads/master@{#13415}

webrtc/modules/audio_coding/neteq/neteq_unittest.cc

@@ -462,13 +462,13 @@ TEST_F(NetEqDecodingTest, MAYBE_TestBitExactness) {
 
   const std::string output_checksum = PlatformChecksum(
       "472ebe1126f41fdb6b5c63c87f625a52e7604e49",
-      "d2a6b6ff54b340cf9f961c7f07768d86b3761073",
+      "36f6fc87c05de077e998173b46b83524de5e8fc2",
       "472ebe1126f41fdb6b5c63c87f625a52e7604e49",
       "f9749813dbc3fb59dae761de518fec65b8407c5b");
 
   const std::string network_stats_checksum = PlatformChecksum(
       "2cf380a05ee07080bd72471e8ec7777a39644ec9",
-      "01be67dc4c3b8e74743a45cbd8684c0535dec9ad",
+      "f50795e25ec2bab2d418c694ab088012776fd450",
       "2cf380a05ee07080bd72471e8ec7777a39644ec9",
       "2cf380a05ee07080bd72471e8ec7777a39644ec9");