[qtc] disable updateinfo plugin

Random crashes seem to be caused by the obsolete updateinfo
plugin.

https://bugreports.qt-project.org/browse/QTCREATORBUG-11262

This also disables the "updates available" pop up, which makes
noticing SDK updates more difficult.

Signed-off-by: Juha Kallioinen <juha.kallioinen@jolla.com>
Merge pull request #23 from sailfish-sdk/disable-updateinfo

[qtc] disable updateinfo plugin