Remove rtc_p2p_unittests from ortc_unittests executable.

These tests are already built into rtc_unittests; they shouldn't be
built into two test executables.

BUG=None
TBR=kjellander@webrtc.org
NOTRY=True

Review-Url: https://codereview.webrtc.org/2820263004
Cr-Commit-Position: refs/heads/master@{#17748}

webrtc/ortc/BUILD.gn

@@ -79,7 +79,6 @@ if (rtc_include_tests) {
       "../base:rtc_base_tests_utils",
       "../media:rtc_unittest_main",
       "../p2p:rtc_p2p",
-      "../p2p:rtc_p2p_unittests",
       "../pc:pc_test_utils",
       "../system_wrappers:metrics_default",
     ]