RFR: 8352162: Update libxml2 to 2.13.8 [v6]

[Jay Bhaskar]

> The upgrade is required to address several known issues from the previous version to improve stability and performance.

Jay Bhaskar has updated the pull request incrementally with one additional commit since the last revision:

  remove unused files

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1785/files
  - new: https://git.openjdk.org/jfx/pull/1785/files/0dbc2e96..5c4b05d0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1785&range=05
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1785&range=04-05

  Stats: 3876 lines in 3 files changed: 0 ins; 3874 del; 2 mod
  Patch: https://git.openjdk.org/jfx/pull/1785.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1785/head:pull/1785

PR: https://git.openjdk.org/jfx/pull/1785