[Pal/Linux-SGX] db_pipes.c: fix segfault due to redundant deletion of pipe

During Graphene initialization, a "server" pipe is created by the IPC thread.
Previously, upon app exit, Graphene's Linux-SGX PAL removed this named pipe.
However, this is not needed and led to occasional segfaults. (Note that Linux
PAL never had this code). This commit simply removes the offending code.

Pal/src/host/Linux-SGX/db_pipes.c

@@ -284,13 +284,6 @@ static int pipe_delete(PAL_HANDLE handle, int access) {
         }
     }
 
-    if (IS_HANDLE_TYPE(handle, pipesrv)) {
-        char buffer[108];
-        pipe_path(handle->pipe.pipeid, buffer, 108);
-        ocall_delete(buffer);
-        return 0;
-    }
-
     if (handle->pipe.fd == PAL_IDX_POISON)
         return 0;