misc: remove references to milestones (grafana#5692)

As part of improving our work process, we are no longer using milestones
for tracking when items get released.

README.md

@@ -100,19 +100,14 @@ launch dependencies to play with Grafana Agent locally.
 
 ## Release cadence
 
-A new minor release is planned every six weeks. You can use the list of
-[Milestones][] to see what maintainers are planning on working on for a given
-release cycle.
+A new minor release is planned every six weeks.
 
-Both the release cadence and the items assigned to a milestone are best-effort:
-releases may be moved forwards or backwards if needed, and items may be moved
-to a different milestone or removed entirely. The planned release dates for
-future minor releases do not change if one minor release is moved.
+The release cadence is best-effort: releases may be moved forwards or backwards
+if needed. The planned release dates for future minor releases do not change if
+one minor release is moved.
 
 Patch and security releases may be created at any time.
 
-[Milestones]: https://github.com/grafana/agent/milestones
-
 ## Community
 
 To engage with the Grafana Agent community:

docs/sources/_index.md

@@ -101,8 +101,6 @@ one minor release is moved.
 
 Patch and security releases may be created at any time.
 
-[Milestones]: https://github.com/grafana/agent/milestones
-
 {{% docs/reference %}}
 [variants]: "/docs/agent/ -> /docs/agent/<AGENT VERSION>/about"
 [variants]: "/docs/grafana-cloud/ -> /docs/grafana-cloud/monitor-infrastructure/agent/about"

docs/sources/_index.md.t

@@ -101,8 +101,6 @@ one minor release is moved.
 
 Patch and security releases may be created at any time.
 
-[Milestones]: https://github.com/grafana/agent/milestones
-
 {{% docs/reference %}}
 [variants]: "/docs/agent/ -> /docs/agent/<AGENT VERSION>/about"
 [variants]: "/docs/grafana-cloud/ -> /docs/grafana-cloud/monitor-infrastructure/agent/about"