glib: Update more gtk-doc comments

Expanding the note for poppler_document_new_from_data() fixes #550.
Formally deprecating it also closes #100 as moot.
7 jobs for gtk-notes in 4 minutes and 25 seconds (queued for 1 second)
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build

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build_android

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build_clang_libcpp

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build_clazy

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build_ubuntu_16_04

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clang_format

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