Upgrade libsrtp to version 2.0 (second attempt)

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 83eb5adfaeec304186bea79434e5d968372660c4..9e11313346af0e44b96d52f51becb3f74663b93a 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -786,19 +786,6 @@ group("gn_only") {
       "//third_party/leveldatabase:leveldb_version_edit_test",
       "//third_party/leveldatabase:leveldb_write_batch_test",
       "//third_party/libjpeg_turbo:simd",
-      "//third_party/libsrtp:rdbx_driver",
-      "//third_party/libsrtp:replay_driver",
-      "//third_party/libsrtp:roc_driver",
-      "//third_party/libsrtp:rtpw",
-      "//third_party/libsrtp:srtp_driver",
-      "//third_party/libsrtp:srtp_test_aes_calc",
-      "//third_party/libsrtp:srtp_test_cipher_driver",
-      "//third_party/libsrtp:srtp_test_datatypes_driver",
-      "//third_party/libsrtp:srtp_test_env",
-      "//third_party/libsrtp:srtp_test_kernel_driver",
-      "//third_party/libsrtp:srtp_test_rand_gen",
-      "//third_party/libsrtp:srtp_test_sha1_driver",
-      "//third_party/libsrtp:srtp_test_stat_driver",
       "//third_party/opus:opus_compare",
       "//third_party/opus:opus_demo",
       "//third_party/opus:test_opus_api",