Fix some invalid attributes in library

cfg/posix.cfg

@@ -27,7 +27,6 @@
   <!-- http://man7.org/linux/man-pages/man2/accept.2.html -->
   <!-- int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen); -->
   <function name="accept">
-    <use-retval/>
     <noreturn>false</noreturn>
     <arg nr="1">
       <not-uninit/>
@@ -37,7 +36,6 @@
     </arg>
     <arg nr="3">
       <not-uninit/>
-      <not-null/>
     </arg>
     <leak-ignore/>
   </function>