Rename ostree-cmdprivate to drop out of introspection

I was looking at our `.gir` and noticed we had the cmdprivate bits
because the pattern for excluding headers is `-private.h`, which
didn't match `cmdprivate.h`.

apidoc/Makefile.am

@@ -71,7 +71,7 @@ IGNORE_HFILES= \
 	ostree-bootloader-grub2.h \
 	ostree-bootloader-syslinux.h \
 	ostree-bootloader-uboot.h \
-	ostree-cmdprivate.h \
+	ostree-cmd-private.h \
 	ostree-core-private.h \
 	ostree-fetcher.h \
 	ostree-gpg-verifier.h \