Remove Pulsar binder docs

The Pulsar binder has been moved to SCSt along with its docs. This
commit deletes the local version of the binder docs and adjusts any
binder links to point to the SCSt docs.

Author: onobc

spring-pulsar-docs/src/main/antora/modules/ROOT/nav.adoc

@@ -10,7 +10,7 @@
 ** xref:reference/pulsar-admin.adoc[]
 ** xref:reference/pulsar-function.adoc[]
 ** xref:reference/observability.adoc[]
-** xref:reference/pulsar-binder.adoc[]
+** https://docs.spring.io/spring-cloud-stream/reference/pulsar/pulsar_binder.html[Spring Cloud Stream Binder for Apache Pulsar]
 * xref:other-resources.adoc[]
 * Appendices
 ** xref:appendix/version-compatibility.adoc[]