cdnfresh.txt: remove archived doc versions (#21062)

Author: qiancai

resources/cdnfresh.txt

@@ -2,14 +2,8 @@ https://docs-download.pingcap.com/pdf/tidb-dev-zh-manual.pdf
 https://docs-download.pingcap.com/pdf/tidb-dev-en-manual.pdf
 https://docs-download.pingcap.com/pdf/tidb-stable-zh-manual.pdf
 https://docs-download.pingcap.com/pdf/tidb-stable-en-manual.pdf
-https://docs-download.pingcap.com/pdf/tidb-v8.4-zh-manual.pdf
-https://docs-download.pingcap.com/pdf/tidb-v8.4-en-manual.pdf
-https://docs-download.pingcap.com/pdf/tidb-v8.3-zh-manual.pdf
-https://docs-download.pingcap.com/pdf/tidb-v8.3-en-manual.pdf
 https://docs-download.pingcap.com/pdf/tidb-v8.1-zh-manual.pdf
 https://docs-download.pingcap.com/pdf/tidb-v8.1-en-manual.pdf
-https://docs-download.pingcap.com/pdf/tidb-v8.0-zh-manual.pdf
-https://docs-download.pingcap.com/pdf/tidb-v8.0-en-manual.pdf
 https://docs-download.pingcap.com/pdf/tidb-v7.6-zh-manual.pdf
 https://docs-download.pingcap.com/pdf/tidb-v7.6-en-manual.pdf
 https://docs-download.pingcap.com/pdf/tidb-v7.5-zh-manual.pdf
@@ -22,10 +16,6 @@ https://docs-download.pingcap.com/pdf/tidb-v6.1-zh-manual.pdf
 https://docs-download.pingcap.com/pdf/tidb-v6.1-en-manual.pdf
 https://docs-download.pingcap.com/pdf/tidb-v5.4-zh-manual.pdf
 https://docs-download.pingcap.com/pdf/tidb-v5.4-en-manual.pdf
-https://docs-download.pingcap.com/pdf/tidb-v5.2-zh-manual.pdf
-https://docs-download.pingcap.com/pdf/tidb-v5.2-en-manual.pdf
-https://docs-download.pingcap.com/pdf/tidb-v5.1-zh-manual.pdf
-https://docs-download.pingcap.com/pdf/tidb-v5.1-en-manual.pdf
 https://docs-download.pingcap.com/pdf/tidb-in-kubernetes-dev-zh-manual.pdf
 https://docs-download.pingcap.com/pdf/tidb-in-kubernetes-dev-en-manual.pdf
 https://docs-download.pingcap.com/pdf/tidb-in-kubernetes-stable-zh-manual.pdf