Fix some issues reported by lintian

Fix some issues reported by lintian

• Trim trailing whitespace. (trailing-whitespace)
• Use secure URI in Homepage field. (homepage-field-uses-insecure-uri)
• Bump debhelper from deprecated 9 to 10. (package-uses-deprecated-debhelper-compat-version)
• Set upstream metadata fields: Bug-Database, Bug-Submit (from ./configure), Repository, Repository-Browse. (upstream-metadata-file-is-missing, upstream-metadata-missing-bug-tracking, upstream-metadata-missing-repository)
• Drop unnecessary dependency on dh-autoreconf. (useless-autoreconf-build-depends)
• Fix day-of-week for changelog entry 0.4.2-1. (debian-changelog-has-wrong-day-of-week)
• Enarmor upstream signing key.
• Re-export upstream signing key without extra signatures. (public-upstream-key-not-minimal)

This merge proposal was created automatically by the Janitor bot. For more information, including instructions on how to disable these merge proposals, see https://janitor.debian.net/lintian-fixes.

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The bot will automatically update the merge proposal to resolve merge conflicts or close the merge proposal when all changes are applied through other means (e.g. cherry-picks). Updates may take several hours to propagate.

Build and test logs for this branch can be found at https://janitor.debian.net/lintian-fixes/pkg/unpaper/08feb860-c80d-48fb-9288-6ff575c12f39.

Debdiff

These changes affect the binary packages:

[The following lists of changes regard files as different if they have different names, permissions or owners.]

Files in second set of .debs but not in first

-rw-r--r--  root/root   /usr/lib/debug/.build-id/75/86c89ebeb8587662df7879716f6e6adebc62d4.debug

Files in first set of .debs but not in second

-rw-r--r--  root/root   /usr/lib/debug/.build-id/3b/ef837a0a5d9d106ef5e9d866cb1166784186c1.debug

Control files of package unpaper: lines which differ (wdiff format)

• Homepage: http​://www.flameeyes.eu/projects/unpaper https​://www.flameeyes.eu/projects/unpaper

Control files of package unpaper-dbgsym: lines which differ (wdiff format)

• Build-Ids: 3bef837a0a5d9d106ef5e9d866cb1166784186c1 7586c89ebeb8587662df7879716f6e6adebc62d4

You can also view the diffoscope diff (unfiltered).