cleanup: remove FIXME and TODO comments

They serve very little purpose and mostly just add noise. Most of them
have been around for a very long time. I read them all before removing
or rephrasing them.

Ref: #3876
Closes #3883

docs/examples/ephiperfifo.c

@@ -518,9 +518,6 @@ int main(int argc _Unused, char **argv _Unused)
   fprintf(MSG_OUT, "Entering wait loop\n");
   fflush(MSG_OUT);
   while(!g_should_exit_) {
-    /* TODO(josh): use epoll_pwait to avoid a race on the signal. Mask the
-     * signal before the while loop, and then re-enable the signal during
-     * epoll wait. Mask at the end of the loop. */
     err = epoll_wait(g.epfd, events, sizeof(events)/sizeof(struct epoll_event),
                      10000);
     if(err == -1) {