The spannable is a CharSequence, which you can manipulate.
This works:
myTextView.setText(noTrailingwhiteLines(html));
private CharSequence noTrailingwhiteLines(CharSequence text) {
while (text.charAt(text.length() - 1) == '\n') {
text = text.subSequence(0, text.length() - 1);
}
return text;
}