Fix some links in the concepts section

This PR fixes the links in the concepts section. Most of the links are
not dead links in English version because there are redirects for them.
However, these links will be broken when localized to any languages
other English.

Where appropriate. this PR also wraps some long lines which are
unfriendly to any localization team that try to catch the differences
between revisions.

content/en/docs/concepts/services-networking/endpoint-slices.md

@@ -249,5 +249,4 @@ implementation in `kube-proxy`.
 
 ## {{% heading "whatsnext" %}}
 
-* Learn about [Enabling EndpointSlices](/docs/tasks/administer-cluster/enabling-endpointslices)
 * Read [Connecting Applications with Services](/docs/concepts/services-networking/connect-applications-service/)

content/en/docs/concepts/services-networking/service.md

@@ -215,7 +215,7 @@ each Service port. The value of this field is mirrored by the corresponding
 Endpoints and EndpointSlice objects.
 
 This field follows standard Kubernetes label syntax. Values should either be
-[IANA standard service names](http://www.iana.org/assignments/service-names) or
+[IANA standard service names](https://www.iana.org/assignments/service-names) or
 domain prefixed names such as `mycompany.com/my-custom-protocol`.
 
 ## Virtual IPs and service proxies