A fixed line break in a text editor (as opposed to HTML!) is a sequence of two bytes (or a single byte, depending on the OS) whose visible consequence is that the line is always broken there, no matter how much space is left. Such a line break is typically produced by pressing the return button while typing. Normally, you can delete it by setting the cursor to the end of the first part and press "Delete", or to the beginning of the second part and press "Backspace". This ought to work in the text entry field of your browser. Inspect the preview to check your success.

An URL will be rendered invalid if a line break is inserted, as you observed. The clicky text, however, can consist of as many lines as you wish.