Fix some issues reported by lintian

Fix some issues reported by lintian

• Add missing ${misc:Depends} to Depends for phonon-backend-gstreamer-common. (debhelper-but-no-misc-depends)
• Set debhelper-compat version in Build-Depends. (uses-debhelper-compat-file)
• Set fields Upstream-Name, Upstream-Contact in debian/copyright.
• Remove obsolete fields Contact, Name from debian/upstream/metadata (already present in machine-readable debian/copyright).

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Build and test logs for this branch can be found at https://janitor.debian.net/lintian-fixes/pkg/phonon-backend-gstreamer/19c84ccd-36b7-407d-8622-b429de20050a.