Remove __ from HAVE_EXTERN_ENVIRON_DECLARED__

I think that the trailing __ got added in false analogy to
HAVE_MACRO__func__, HAVE_MACRO__FUNC__, and HAVE_MACRO__FUNCTION__.
But those macros actually indicate the presence of __func__,
__FUNC__, and __FUNCTION__ respectively.  The __ at the end of
HAVE_EXTERN_ENVIRON_DECLARED would only be appropriate if the
environ were declared__, whatever that means.

(As a side-note, HAVE_MACRO__func__ and so on should probably be
renamed HAVE_MACRO___func__ and so on.  But that can wait.)

This is an identifier renaming only.

configure.in

@@ -1138,7 +1138,7 @@ if test "$tor_cv_have_FUNCTION_macro" = 'yes'; then
 fi
 
 if test "$tor_cv_have_environ_declared" = 'yes'; then
-  AC_DEFINE(HAVE_EXTERN_ENVIRON_DECLARED__, 1,
+  AC_DEFINE(HAVE_EXTERN_ENVIRON_DECLARED, 1,
            [Defined if we have extern char **environ already declared])
 fi
 

src/common/compat.c

@@ -1712,7 +1712,7 @@ make_path_absolute(char *fname)
 }
 
 #ifndef HAVE__NSGETENVIRON
-#ifndef HAVE_EXTERN_ENVIRON_DECLARED__
+#ifndef HAVE_EXTERN_ENVIRON_DECLARED
 /* Some platforms declare environ under some circumstances, others don't. */
 extern char **environ;
 #endif