paths.h: remove the _BSD_SOURCE guard

It seems like glibc also has paths.h and m4 fails to bootstrap
without _PATH_BSHELL.

This file really needs some cleanup btw, since most is actually
irrelevant or incorrect for Haiku.

headers/compatibility/bsd/paths.h

@@ -38,9 +38,6 @@
 #define	_PATHS_H_
 
 
-#ifdef _BSD_SOURCE
-
-
 #include <sys/cdefs.h>
 
 /* Default search path. */
@@ -141,7 +138,4 @@ __END_DECLS
 #endif /* RESCUE */
 
 
-#endif
-
-
 #endif /* !_PATHS_H_ */