Fix some issues reported by lintian

Fix some issues reported by lintian

• Trim trailing whitespace. (trailing-whitespace)
• Remove unnecessary Team Upload line in changelog.
• Drop unnecessary dependency on dh-autoreconf.
• Update standards version to 4.6.1, no changes needed. (out-of-date-standards-version)
• Set upstream metadata fields: Repository. (upstream-metadata-file-is-missing)
• Update standards version to 4.6.2, no changes needed. (out-of-date-standards-version)

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/66/eee5bc70fcc8d4059cddf1b17e802835848dc7.debug

Files in first set of .debs but not in second

-rw-r--r--  root/root   /usr/lib/debug/.build-id/60/25b9d97b96487550a0358e849016638d8a7df6.debug

No differences were encountered between the control files of package **xmppc**

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

• Build-Ids: 6025b9d97b96487550a0358e849016638d8a7df6 66eee5bc70fcc8d4059cddf1b17e802835848dc7

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Build and test logs for this branch can be found at https://janitor.debian.net/run/d145ea90-cac3-4651-ba3c-f7577010b273.