dev: delete gumbo_normalize_svg_tagname (#3402)

**What problem is this PR intended to solve?**

It's unused. See discussion at #2950

gumbo-parser/src/nokogiri_gumbo.h

@@ -318,21 +318,6 @@ const char* gumbo_normalized_tagname(GumboTag tag);
  */
 void gumbo_tag_from_original_text(GumboStringPiece* text);
 
-/**
- * Fixes the case of SVG elements that are not all lowercase. This is
- * not done at parse time because there's no place to store a mutated
- * tag name. `tag_name` is an enum (which will be `TAG_UNKNOWN` for most
- * SVG tags without special handling), while `original_tag_name` is a
- * pointer into the original buffer. Instead, we provide this helper
- * function that clients can use to rename SVG tags as appropriate.
- * Returns the case-normalized SVG tagname if a replacement is found, or
- * `NULL` if no normalization is called for. The return value is static
- * data and owned by the library.
- *
- * @see https://html.spec.whatwg.org/multipage/parsing.html#parsing-main-inforeign
- */
-const char* gumbo_normalize_svg_tagname(const GumboStringPiece* tagname);
-
 /**
  * Converts a tag name string (which may be in upper or mixed case) to a
  * tag enum.

gumbo-parser/src/parser.c

@@ -1962,14 +1962,6 @@ static void merge_attributes (
 #endif
 }
 
-const char* gumbo_normalize_svg_tagname(const GumboStringPiece* tag) {
-  const StringReplacement *replacement = gumbo_get_svg_tag_replacement (
-    tag->data,
-    tag->length
-  );
-  return replacement ? replacement->to : NULL;
-}
-
 // https://html.spec.whatwg.org/multipage/parsing.html#adjust-foreign-attributes
 // This destructively modifies any matching attributes on the token and sets the
 // namespace appropriately.