It's hard to tell from the distance...
The error message is unusual to me, I am not a Linux specialist. I did not even know of a "builddir"... In case of such strange messages, I normally do a clean rebuild of the project ("Run" > "Build", or "Run" > "Clean up and Build"). If this does not help, I do a clean rebuild of the IDE. "Tools" > "Configure Build Lazarus" > in the "Clean up" box check "Clean all" and "Switch to automatic mode after building" > "Build".
Depending on how you installed Lazarus, however, rebuilding the IDE in Linux may be easy or a pain... - there are numerous threads in the forum about such problems.
How did you use the "old" package in your project? Did you add the path to it in the "Other unit files" project options? That's the way Delphi does it. Remove the path to the playsound package from "Other unit files". Delete the output directory of the project (listed as "Unit output directory" on the same page of the project options) and compile again. Or did you add the package to the "required packages" of the project (in the Project Options)? That's the Lazarus way. Just delete the package from the "required packages" node of the project tree. It would not be harmful to delete the output directory, too.
You should also get rid of the package. Did you "use" > "install" as I told you in the previous message? In this case, go to "Package" > "Install/uninstall packages", select the package in the LEFT package list, click "Uninstall selection", then "Rebuild IDE". After a while the IDE restarts, and the package is gone. It still exists on the disk though, you can simple delete the files now.