make: doc/sequence_charts: use wildcards for EXTRA_DIST and CLEANFILES

Both EXTRA_DIST and CLEANFILES had missing entries. It is easy to
forget to keep them up to date. Rather use wildcards to always pick up
all relevant files.

(Not adding *.dot because there are no .dot charts here, yet.)

Change-Id: I3a18e4608a310169d7c9cd9c1b8ac9015a990920

doc/sequence_charts/Makefile.am

@@ -4,17 +4,11 @@ all:
 charts: msc dot
 
 EXTRA_DIST = \
-	inter_bsc_ho.msc \
-	inter_msc_ho.msc \
-	mncc_call_fsm.msc \
-	call_reestablishment.msc \
+	$(srcdir)/*.msc \
 	$(NULL)
 
 CLEANFILES = \
-	inter_bsc_ho.png \
-	inter_msc_ho.png \
-	mncc_call_fsm.png \
-	voice_call_full.png \
+	$(builddir)/*.png \
 	$(NULL)
 
 msc: \