Fix some issues reported by lintian

Fix some issues reported by lintian

• Set upstream metadata fields: Bug-Database. (upstream-metadata-missing-bug-tracking)
• Drop unnecessary dependency on dh-autoreconf.
• Remove obsolete fields Contact, Name from debian/upstream/metadata (already present in machine-readable debian/copyright).
• 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 (out-of-date-standards-version)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/88/fd812f3946471449b176832ab1f477d9982a44.debug

Files in first set of .debs but not in second

-rw-r--r--  root/root   /usr/lib/debug/.build-id/9f/bae40aae4dbb8c9512c3ec61f1d7539957767b.debug

No differences were encountered between the control files of package **xilinx-bootgen**

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

• Build-Ids: 9fbae40aae4dbb8c9512c3ec61f1d7539957767b 88fd812f3946471449b176832ab1f477d9982a44

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Build and test logs for this branch can be found at https://janitor.debian.net/lintian-fixes/pkg/xilinx-bootgen/7c43f8a8-ca91-4e8b-902b-e75f6ca1f693.