Rename gtest_exclude for rtc_pc_unittests

This was forgotten in https://codereview.webrtc.org/1694813002/
Also clean up no-longer-used files for libjignle_unittest (renamed
to rtc_unittests a long time ago).

BUG=webrtc:5419
TBR=pbos@webrtc.org

Review URL: https://codereview.webrtc.org/1698123002 .

Cr-Commit-Position: refs/heads/master@{#11625}

tools/valgrind-webrtc/gtest_exclude/libjingle_unittest.gtest-memcheck.txt

@@ -1,5 +0,0 @@
-# Fails when run under memcheck
-# https://code.google.com/p/webrtc/issues/detail?id=1976
-PhysicalSocketTest.TestUdpReadyToSendIPv4
-ThreadTest.Release
-

tools/valgrind-webrtc/gtest_exclude/libjingle_unittest.gtest-memcheck_mac.txt

@@ -1,7 +0,0 @@
-# Crashes the kernel when run under memcheck on Mac.
-# No bug is filed in relation to this since it's unlikely we can fix it.
-# There are several tests disabled in the libjingle code with similar comments,
-# without bugs assigned to them.
-# Example: talk/base/physicalsocketserver_unittest.cc
-NatTest.TestVirtualIPv*
-PosixSignalDeliveryTest.*