Your ~/Pictures/Lightroom folder contains original .LRCAT files for Lightroom 2, 4, and 5 as well as Lightroom 6. There is also a separate catalog folder, ~/Pictures/aprilcomb. The LR default catalog you want to have opened automatically whenever Lightroom runs is not set (Lightroom Preferences > General tab).
Presuming that your intent is to use Lightroom 6 and the latest catalog in the ~/Pictures/Lightroom folder, click the checkbox next to "Always load this catalog on startup" and click Open. In the future, double-clicking the Lightroom app icon will automatically load that catalog, bypassing the catalog selection dialog. You can change this setting in Lightroom Preferences or by calling up the catalog selection dialog manually again using File > Open Catalog.
Outside of Lightroom, you can go into that folder and delete the .LRCAT files for LR 2, 4, and 5 since they're just sitting there wasting space at this point. There's really no point in keeping them around unless you still have those older versions of Lightroom installed and want to switch back to one of them for some reason.
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