common/json_parse_simple: drop redundant and wrong json_str_to_u64()

The json_str_to_u64() function contains incorrect logic. It chops one character
off of the beginning and end of the JSMN token and then parses the remainder as
a u64, but JSMN_STRING tokens already do not include the enclosing quotation
marks, so json_str_to_u64() would actually parse the JSON string "1234" into
the integer 23. Oops! Also note that it would simply fail on all input strings
shorter than two characters since tok->end would wind up *before* tok->start.

Just drop the function entirely. It was only used in one place, and that place
explicitly doesn't care whether its input is a JSON number or a numeric string,
and it was already calling json_to_u64() as an alternative, and that function
already accepts both JSON strings and JSON numbers as input, so the call to
json_str_to_u64() would have been entirely redundant if it had been correct.

Changelog-Fixed: The `keysend` command no longer corrupts the type numbers of extra TLVs when they are specified as numeric strings longer than 2 digits.

common/json_parse_simple.c

@@ -109,19 +109,6 @@ bool json_to_s64(const char *buffer, const jsmntok_t *tok, s64 *num)
 	return true;
 }
 
-bool json_str_to_u64(const char *buffer, const jsmntok_t *tok, u64 *num)
-{
-	jsmntok_t temp;
-	if (tok->type != JSMN_STRING)
-		return false;
-
-	temp = *tok;
-	temp.start += 1;
-	temp.end -= 1;
-
-	return json_to_u64(buffer, &temp, num);
-}
-
 bool json_to_double(const char *buffer, const jsmntok_t *tok, double *num)
 {
 	char *end;