test: check for button presses in middlebutton_device_remove_while_one_is_down

This test was failing when using Valgrind randomly. Check for button
pressed explicitly to avoid issues.

Signed-off-by: José Expósito <jose.exposito89@gmail.com>
68 jobs for fix-test-middlebutton_device_remove_while_one_is_down in 27 minutes and 56 seconds (queued for 4 seconds)
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