[browser] Cleanup browser.helperApps.deleteTempFileOnExit preference. JB#49155
[browser] Cleanup browser.helperApps.deleteTempFileOnExit preference. JB#49155

sailfishos/sailfish-browser,sailfishos/sailfish-browser,sailfishos/sailfish-browser,sailfishos/sailfish-browser,sailfishos/sailfish-browser