Remove top-level const from parameters in function declarations.

This is a safe cleanup change since top-level const applied to
parameters in function declarations (that are not also
definitions) are ignored by the compiler. Hence, such changes do
not change the type of the declared functions and are simply
no-ops.

Bug: webrtc:13610
Change-Id: Ibafb92c45119a6d8bdb6f9109aa8dad6385163a9
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/249086
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Ali Tofigh <alito@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35802}

rtc_base/string_encode.h

diff --git a/rtc_base/string_encode.h b/rtc_base/string_encode.h
index d636f7f..c63d527 100644
--- a/rtc_base/string_encode.h
+++ b/rtc_base/string_encode.h
@@ -80,7 +80,7 @@
 // duplicates of delimiter ignored. Return false if the delimiter could not be
 // found, otherwise return true.
 bool tokenize_first(absl::string_view source,
-                    const char delimiter,
+                    char delimiter,
                     std::string* token,
                     std::string* rest);