Fixup 71623b88: change semantics of "delete" LFUNs again

Fixup 71623b88: change semantics of "delete" LFUNs again

Instead of specifying "force" to disable the deletion protection
mechanism, invert the default so that "confirm" is needed to activate
it. The idea is to keep the lfun reasonable for scripting and add a
special argument for interactive use.

Document in release notes.

Update LFUN.lyx documentation

Update bind files.

Add conversion step to prefs2prefs_lfun.py.