lib/pull: Split verify_bindings() out into a cmdprivate method

It will be used by the fsck utility in future. We could expose it
publicly in future too, if needed.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #1347
Approved by: cgwalters

apidoc/Makefile.am

@@ -83,6 +83,7 @@ IGNORE_HFILES= \
 	ostree-metalink.h \
 	ostree-repo-file-enumerator.h \
 	ostree-repo-private.h \
+	ostree-repo-pull-private.h \
 	ostree-repo-static-delta-private.h \
 	ostree-sysroot-private.h \
 	ostree-tls-cert-interaction.h \