Baremetal config: Remove MBEDTLS_SSL_TICKETS_C

This doesn't make a difference after link time optimization because
tickets aren't used, but it yields more accurate code-size figures
from baremetal.sh.
diff --git a/configs/baremetal.h b/configs/baremetal.h
index 11292e1..f8ad61c 100644
--- a/configs/baremetal.h
+++ b/configs/baremetal.h
@@ -147,7 +147,6 @@
 #define MBEDTLS_SSL_MAX_CONTENT_LEN             2048
 
 /* Server-side only */
-#define MBEDTLS_SSL_TICKET_C
 #define MBEDTLS_SSL_SRV_C
 
 #if defined(MBEDTLS_USER_CONFIG_FILE)