Delete sigcheck.c since it appears unused (#1723)

diff --git a/Include/pyerrors.h b/Include/pyerrors.h
index 4540385..fcaba85 100644
--- a/Include/pyerrors.h
+++ b/Include/pyerrors.h
@@ -352,7 +352,7 @@
 #endif
 
 
-/* In sigcheck.c or signalmodule.c */
+/* In signalmodule.c */
 PyAPI_FUNC(int) PyErr_CheckSignals(void);
 PyAPI_FUNC(void) PyErr_SetInterrupt(void);