Remove needless type casting.

CLA: trivial
Reviewed-by: NKurt Roeckx <kurt@openssl.org>
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3627)

crypto/x509/by_file.c

@@ -42,12 +42,12 @@ static int by_file_ctrl(X509_LOOKUP *ctx, int cmd, const char *argp,
                         long argl, char **ret)
 {
     int ok = 0;
-    char *file;
+    const char *file;
 
     switch (cmd) {
     case X509_L_FILE_LOAD:
         if (argl == X509_FILETYPE_DEFAULT) {
-            file = (char *)getenv(X509_get_default_cert_file_env());
+            file = getenv(X509_get_default_cert_file_env());
             if (file)
                 ok = (X509_load_cert_crl_file(ctx, file,
                                               X509_FILETYPE_PEM) != 0);