Replace remaining mysignal() with signal().

These seem to have been missed during the replacement of mysignal
with #define signal in commit 5ade9ab.  Both include the requisite
headers to pick up the #define.
diff --git a/entropy.c b/entropy.c
index 9305f89..14b98f1 100644
--- a/entropy.c
+++ b/entropy.c
@@ -108,7 +108,7 @@
 		    strlen(socket_path) + 1;
 	}
 
-	old_sigpipe = mysignal(SIGPIPE, SIG_IGN);
+	old_sigpipe = signal(SIGPIPE, SIG_IGN);
 
 	errors = 0;
 	rval = -1;
@@ -158,7 +158,7 @@
 
 	rval = 0;
 done:
-	mysignal(SIGPIPE, old_sigpipe);
+	signal(SIGPIPE, old_sigpipe);
 	if (fd != -1)
 		close(fd);
 	return rval;