Prune changelogs after 9.1.4 release

docs/changelog/133398.yaml

@@ -1,5 +0,0 @@
-pr: 133398
-summary: "Aggs: Fix CB on reduction phase"
-area: Aggregations
-type: bug
-issues: []

docs/changelog/133752.yaml

@@ -1,5 +0,0 @@
-pr: 133752
-summary: Avoid stale enrich results after policy execution
-area: Ingest Node
-type: bug
-issues: []

docs/changelog/133775.yaml

@@ -1,5 +0,0 @@
-pr: 133775
-summary: Remove Transfer-Encoding from HTTP request with no content
-area: Network
-type: bug
-issues: []