Mail: fixed a comment.

There's no loc_conf in the mail module.

src/mail/ngx_mail.c

diff --git a/src/mail/ngx_mail.c b/src/mail/ngx_mail.c
index 350d2cd..5a7cb6b 100644
--- a/src/mail/ngx_mail.c
+++ b/src/mail/ngx_mail.c
@@ -131,8 +131,7 @@
 
 
     /*
-     * create the main_conf's, the null srv_conf's, and the null loc_conf's
-     * of the all mail modules
+     * create the main_conf's and the null srv_conf's of the all mail modules
      */
 
     for (m = 0; ngx_modules[m]; m++) {