Yeah I was surprised they took it down. I think it's a foolish knee jerk reaction and is patronising towards readers.
Ironically there is know nothing to put the current spike of interest in context as you can't read the letter on the guardian website.
I'm actually really unimpressed with the guardians action - they don't respect their readers and clearly no longer believe in freedom of speech. They could have modified the article to put the letter in context themselves rather than link to a 20 year old article criticising it. It also makes it hard for those who want to push back against the letter and answer those who are pushing it.
It's not immovable, it's just locked so you don't accidentally move it by clicking and dragging. Try right locking on the bar in a blank area lower down - the right click menu should have an option for moving it.