Windows build fix.
Windows build fix.

Broke with d3c0557444928b8a3b2812622b7d1137f81e05aa
Remove the logic for setting jom as default or not, and just set it as
default, since the new AbstractMsvcToolChain::makeCommand uses nmake as
a fallback if jom is not found.

Task-number: QTCREATORBUG-7876
Change-Id: Ia96c2449863fbbd027fbaf003d75bb6155206289
Reviewed-by: Oliver Wolff <bfa2c373f7b4cae624ec1928f54bc38b8cd9f442@nokia.com>

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