Delete redundant function rtc::tokenize_with_empty_tokens

It was identical to rtc::split.

Bug: webrtc:6424
Change-Id: I1118ad34050c0eb324ade347c97174f3ad4b39a7
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/231234
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#34946}

rtc_base/string_encode.h

@@ -72,11 +72,6 @@ size_t tokenize(const std::string& source,
                 char delimiter,
                 std::vector<std::string>* fields);
 
-// Tokenize, including the empty tokens.
-size_t tokenize_with_empty_tokens(const std::string& source,
-                                  char delimiter,
-                                  std::vector<std::string>* fields);
-
 // Extract the first token from source as separated by delimiter, with
 // duplicates of delimiter ignored. Return false if the delimiter could not be
 // found, otherwise return true.