feat(libunistring): remove docs (#31931)

Splitt docs into own docs package

Fixes:
shyim/wolfi-php#519

Related:

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#### For new package PRs only
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#### For new version streams
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When updating packages part of base images (i.e.
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libunistring.yaml

@@ -1,7 +1,7 @@
 package:
   name: libunistring
   version: "1.3"
-  epoch: 0
+  epoch: 1
   description: Library for manipulating Unicode strings and C strings
   copyright:
     - license: GPL-2.0-or-later OR LGPL-3.0-or-later
@@ -41,6 +41,13 @@ pipeline:
   - uses: strip
 
 subpackages:
+  - name: libunistring-doc
+    pipeline:
+      - uses: split/manpages
+      - runs: |
+          mkdir -p ${{targets.subpkgdir}}/usr/share/doc
+          mv ${{targets.destdir}}/usr/share/doc/libunistring ${{targets.subpkgdir}}/usr/share/doc/libunistring
+
   - name: libunistring-static
     pipeline:
       - uses: split/static