Delete more rtc_base/stringutils.*

Delete nonnull, strchr, strchrn, strcatn, strlenn and Traits.

Bug: webrtc:6424
Change-Id: I3b5a48cb71c6de33635f25ef64d941c422ad0881
Reviewed-on: https://webrtc-review.googlesource.com/c/106341
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25232}
diff --git a/rtc_base/win32.cc b/rtc_base/win32.cc
index e138752..e3482e3 100644
--- a/rtc_base/win32.cc
+++ b/rtc_base/win32.cc
@@ -224,8 +224,8 @@
       *(readcursor + 2) != 0) {
     // Check for periods, which we'll take as a sign of v4 addresses.
     const char* addrstart = readcursor + 2;
-    if (rtc::strchr(addrstart, ".")) {
-      const char* colon = rtc::strchr(addrstart, "::");
+    if (strchr(addrstart, '.')) {
+      const char* colon = strchr(addrstart, ':');
       if (colon) {
         uint16_t a_short;
         int bytesread = 0;