add_c_file: Fix "control line not preceded by a blank line"

Fix dirauth and relay module include.am add_c_file.py
"control line not preceded by a blank line" errors.

Also remove a duplicate ADD_C_FILE: SOURCES in the relay module.

Obviously correct fixes to already-reviewed code.

src/feature/dirauth/include.am

 
 # The Directory Authority module.
+
 # ADD_C_FILE: INSERT SOURCES HERE.
 MODULE_DIRAUTH_SOURCES =					\
 	src/feature/dirauth/authmode.c				\

src/feature/relay/include.am

 
-# ADD_C_FILE: INSERT SOURCES HERE.
+# Legacy shared relay code: migrate to the relay module over time
 LIBTOR_APP_A_SOURCES += 			\
 	src/feature/relay/dns.c			\
 	src/feature/relay/ext_orport.c		\
@@ -9,6 +9,7 @@ LIBTOR_APP_A_SOURCES += 			\
 	src/feature/relay/selftest.c
 
 # The Relay module.
+
 # ADD_C_FILE: INSERT SOURCES HERE.
 MODULE_RELAY_SOURCES = 						\
 	src/feature/relay/routermode.c				\