tweaks: remove two pointless re-inclusion guards

The nano.h file is included only by proto.h, and the proto.h file is
included just once by each src/*.c file.  The include guards for these
two header files serve no purpose.

(Include guards are useful when you have bunches of header files
and several of them include others from amongst themselves.)

src/nano.h

@@ -19,9 +19,6 @@
  *                                                                        *
  **************************************************************************/
 
-#ifndef NANO_H
-#define NANO_H 1
-
 #ifdef HAVE_CONFIG_H
 #include <config.h>
 #endif
@@ -650,5 +647,3 @@ enum
 
 /* The largest size_t number that doesn't have the high bit set. */
 #define HIGHEST_POSITIVE ((~(size_t)0) >> 1)
-
-#endif /* !NANO_H */

src/proto.h

@@ -18,9 +18,6 @@
  *                                                                        *
  **************************************************************************/
 
-#ifndef PROTO_H
-#define PROTO_H 1
-
 #include "nano.h"
 
 /* All external variables.  See global.c for their descriptions. */
@@ -699,5 +696,3 @@ void flip_newbuffer(void);
 #endif
 void discard_buffer(void);
 void do_cancel(void);
-
-#endif /* !PROTO_H */