LibC: Don't clear static storage during endgrent

The POSIX documentation for `endgrent` only mentions that it "closes
the group database", not that it clears the backing storage for return
values. This means that applications might make use of the returned
values even after closing the group database itself. This includes our
own implementations for `getgrnam` and `getgrgid`.

The specification also states that "the storage areas might be
overwritten by a subsequent call to `getgrgid`, `getgrnam`, or
`getgrent`". This implies that `getgrgid` and `getgrnam` aren't meant
to have their own static storage and instead rely on the storage of
`getgrent`.

Userland/Libraries/LibC/grp.cpp

@@ -47,13 +47,6 @@ void endgrent()
         fclose(s_stream);
         s_stream = nullptr;
     }
-
-    memset(&s_group, 0, sizeof(s_group));
-
-    s_name = {};
-    s_passwd = {};
-    s_members = {};
-    s_members_ptrs = {};
 }
 
 struct group* getgrgid(gid_t gid)