tests: Move userdb test out of libdbus

All the functions under test turn out to be DBUS_PRIVATE_EXPORT already.

Signed-off-by: Simon McVittie <smcv@collabora.com>
12 jobs for break-out-more-tests in 9 minutes and 7 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Build
manual #396672
allowed to fail manual
build:buster
passed #396666
build:cmake

00:04:49

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build:debug

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manual #396668
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build:i686-w64-mingw32-cmake
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build:i686-w64-mingw32-debug

00:03:49

manual #396671
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build:jessie
manual #396665
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build:legacy
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build:production

00:06:28

manual #396664
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build:reduced
passed #396669
build:x86_64-w64-mingw32

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passed #396670
build:x86_64-w64-mingw32-cmake-debug

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manual #396673
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build:xenial