debian/rules: Don't fail the build for deprecated declarations

Jeremy Bícharequested to merge
jbicha/guacamole-server:ftbfs-1002194 into master

Closes: https://bugs.debian.org/1002194

I went ahead and uploaded this a 0-day NMU, so you should probably grab the release tag debian/1.3.0-1.1 from my fork too.

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