Delete unused variants of rtc::tokenize

Bug: webrtc:6424
Change-Id: I16f3313e242e0e9ee2039a79d3a8b50c28190832
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/231129
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#34918}

rtc_base/string_encode.h

@@ -77,24 +77,6 @@ size_t tokenize_with_empty_tokens(const std::string& source,
                                   char delimiter,
                                   std::vector<std::string>* fields);
 
-// Tokenize and append the tokens to fields. Return the new size of fields.
-size_t tokenize_append(const std::string& source,
-                       char delimiter,
-                       std::vector<std::string>* fields);
-
-// Splits the source string into multiple fields separated by delimiter, with
-// duplicates of delimiter ignored. Trailing delimiter ignored. A substring in
-// between the start_mark and the end_mark is treated as a single field. Return
-// the size of fields. For example, if source is "filename
-// \"/Library/Application Support/media content.txt\"", delimiter is ' ', and
-// the start_mark and end_mark are '"', this method returns two fields:
-// "filename" and "/Library/Application Support/media content.txt".
-size_t tokenize(const std::string& source,
-                char delimiter,
-                char start_mark,
-                char end_mark,
-                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.