AG-43979 Fix max-length default claim and note title in HTML filtering docs

[slvvko]

What

Follow-up to #927 (Document raw-text :contains() arguments of HTML filtering rules), addressing the two review comments left by @maximtop after that PR was merged ("A few nits inline, can go into a follow-up").

• docs/general/ad-filtering/create-own-filters.md
  • Special attributes → max-length: removed the Default value paragraph ("If this parameter is not specified, the max-length is considered to be 8192.").
  • Pseudo-classes → :contains(): dropped the redundant "Note" title, now a plain :::note like the one above.

Why

The max-length paragraph stated a default that neither CoreLibs nor the extension has, and it contradicted the [tag-content] → :contains() conversion table right above it: $$div[tag-content="banner"] converts to $$div:contains(banner) with no length constraint, and the agtree converter emits a length regexp only when [max-length] is present. No user-visible rule syntax changes — the text simply no longer claims a default.

The :::note Note title carried no information, so it was dropped to match the untitled :::note used earlier in the same article.

Verification

• npx markdownlint-cli2 docs/general/ad-filtering/create-own-filters.md — 0 errors.
• grep -rn "8192" docs/ — no occurrences left.
• Diff is 2 hunks: 5 lines removed, 1 line changed.

Notes

• Related follow-up outside this repo: tsurlfilter's packages/agtree/src/converter/cosmetic/html.ts still has a code comment claiming the same 8192 default (line 56 on master); it should be corrected there separately.

[github-actions]

Preview was deployed to: https://pull-request-949.kb-adg.pages.dev/