Fix typos in C header files

Signed-off-by: Tobias Nießen <tniessen@tnie.de>
diff --git a/include/mbedtls/ssl_ticket.h b/include/mbedtls/ssl_ticket.h
index bf5fc97..a882eed 100644
--- a/include/mbedtls/ssl_ticket.h
+++ b/include/mbedtls/ssl_ticket.h
@@ -97,7 +97,7 @@
  *                  Recommended value: 86400 (one day).
  *
  * \note            It is highly recommended to select a cipher that is at
- *                  least as strong as the the strongest ciphersuite
+ *                  least as strong as the strongest ciphersuite
  *                  supported. Usually that means a 256-bit key.
  *
  * \note            The lifetime of the keys is twice the lifetime of tickets.