Well, just figured it out by using different search terms: https://stackoverflow.com/questions/10757671/how-to-remove-line-breaks-no-characters-from-the-string
To remove HTML breaks from PHP returns (not actually called “line breaks” because they may get confused with the br tag) you’d have to use something like str_replace() with the \r and \n characters which are PHP breaks. In my case, this is what I did: declared a variable for str_replace() with apply_filters() on the post content I needed:
<?php $content = str_replace(array("\r", "\n"), "", apply_filters('the_content', get_post_field('post_content', 44))); ?>
Then echoed that variable on the code I already had:
$(function(){
$('p.office a').html('hover here <div id="tooltip"><?php echo $content ?></div>');
});