Stop disabling -Wattributes (#41174)

In one of the reviews one of the LLMs noticed that the pragma is set but
never unset, so it remains in effect for the rest of the translation
unit. From the comment, it's not clear how old those "old compilers"
were, so let's try if things work without this workaround.

src/basic/static-destruct.h

@@ -12,8 +12,6 @@ typedef void (*free_func_t)(void *p);
  * variables declared in .so's, as the list is private to the same linking unit. But maybe that's a good thing. */
 
 #define _common_static_destruct_attrs_                                  \
-        /* Older compilers don't know "retain" attribute. */            \
-        _Pragma("GCC diagnostic ignored \"-Wattributes\"")              \
         /* The actual destructor structure we place in a special section to find it. */ \
         _section_("SYSTEMD_STATIC_DESTRUCT")                            \
         /* Use pointer alignment, since that is apparently what gcc does for static variables. */ \