Remove unnecessary (char *) casts [string]

Remove (char *) casts around string functions where the arguments or
result already have the right type and the cast is useless (or worse,
potentially casts away a qualifier, but this doesn't appear to be the
case here).

Reviewed-by: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
Discussion: https://www.postgresql.org/message-id/flat/fd1fcedb-3492-4fc8-9e3e-74b97f2db6c7%40eisentraut.org

src/interfaces/ecpg/pgtypeslib/common.c

@@ -19,7 +19,7 @@ pgtypes_alloc(long size)
 char *
 pgtypes_strdup(const char *str)
 {
-	char	   *new = (char *) strdup(str);
+	char	   *new = strdup(str);
 
 	if (!new)
 		errno = ENOMEM;