All generated .c are named like their .h, except for qmp-marshal.c and
qmp-commands.h.  To add to the confusion, tests-qmp-commands.c falsely
matches generated test-qmp-commands.h.

Get rid of this unnecessary complication.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Message-Id: <20180211093607.27351-19-armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: NMichael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: NEric Blake <eblake@redhat.com>