Remove unneeded call to CatalogChanged().

This call is relatively expensive, so avoid it when not necessary.
RefreshControls() below does the same already.
Reset default invalid values of Team headers for new files.

Don't preserve the warnings-issuing, invalid value of Language-Team:
"LANGUAGE <LL@li.org>" for Language-Team.

Poedit used to always clear team metadata for new files.  That was too
much, so 625ce49ca790 removed that.  That was too little, the desirable
middle ground is to preserve meaningful entries, but clear the (invalid)
defaults.  The defaults are useless and only produce warnings that
pretty much nobody cares about these days.

See also 625ce49ca790