Don’t ‘normalise’ hints for bare ‘no feature’

Don’t ‘normalise’ hints for bare ‘no feature’

‘Normalise’ in this case means to set $^H to indicate that features
are in %^H (FEATURE_BUNDLE_CUSTOM) and to make %^H contain the current
feature set.

Since ‘no feature’ sets the default feature bundle in $^H, this is
unnecessary in that case.