fix(solutions): fix: more memory issues thanks to -fsanitize=address flag with gcc

challenges/look-and-say-sequence-conway/solutions/c/function/character.h

@@ -13,13 +13,4 @@
  */
 void character_append(char* string, char character);
 
-/**
- * @brief Append many characters to a string, assuming string points to an array
- * with enough space.
- *
- * @param string
- * @param characters
- */
-void character_append_many(char* string, char* characters);
-
 #endif