Replace multiple matching instances within paragraph?

I'm trying to use a regex to replace all instances of a given match (in this case line breaks) within paragraph markings. I cannot simply replace all <br/> instances in my document because some are important to have.

The document layout looks something like this:
I would like it to become:
While I am pretty good at advanced regular expressions, I am thinking that what I'm asking for here would require back references to replace the <br/>'s with nothing.

Could somebody here show me how to do this, or has there been a thread about this already?

So far I have started with:
and that seems to work in this regex tester program I am using, but what would I enter into the replace field in Calibre for this? Do I need back-references?

Thanks,
Chris