Fix some issues reported by lintian

Fix some issues reported by lintian

• Trim trailing whitespace. (trailing-whitespace)
• Strip unusual field spacing from debian/control. (debian-control-has-unusual-field-spacing)
• debian/copyright: use spaces rather than tabs to start continuation lines. (tab-in-license-text)

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Build and test logs for this branch can be found at https://janitor.debian.net/lintian-fixes/pkg/libdap/00264581-c76d-4598-81fa-fcd5c6080a51.

These changes affect the binary packages; see the debdiff

You can also view the diffoscope diff (unfiltered).