Notepad++ Delete Lines with Find & Replace

Use the "Extended" setting in the Replace window (not "Regular expression": I'm sure there's a way to do it with Regular expression, but using "Extended" works fine).
Enter ".pPrev.\r\n" in the "Find what" field, and leave the "Replace what" field blank. This will include the \r\n characters in the match and delete the whole line.

Using the "Regular expression search" option in the Find & Replace window:

Define the regex Find string that you are looking for, and include the \xd?\xa "end-of-line" characters in the match.

If want to delete these line brakes then leave the Replace string blank.

Note, the carriage return character is optional (\xd?), because you could have lines ending with no carriage return and only a line feed character \xa.

The general principle whichever editor you're using is that you need to include the new line characters (\r\n assuming Windows line endings) in your search so that they will be included in the replacement and thus removed.

In Notepad++ this is made a bit more confusing by the 2 different search and replace commands. See this Wiki page for details: Replacing Newlines in Notepad++

I only had an old version of Notepad++ to hand so had to use Extended Search (accessed via ^R), making sure Regular Expr was unticked and using ^M to insert the new line character into the Find field. However if you make sure you're using Notepad++ 4.9 or later you should be able to use \r and \n in the regexp mode.

You can actually select the newline by moving your cursor from the end of one line to the beginning of the next:

first line(from here)
(to here)decond line
third line

Then press ctrl+h while the new line is selected, and replace with nothing. This will delete all the newlines.