Do not use sal/log.hxx in extensions

"For now, this functionality should only be used internally within LibreOffice.
It may change again in a future version." (sal/log.hxx)

And the condition that was checked already causes a RuntimeException, so was
somewhat redundant anyway.  Thanks to mstahl for spotting this.

Change-Id: I51cc4e75b3d3ffc97943613c61cb93c1fb48e59b