GIMP Script-fu

sg-ungroup-layer
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Command:
Ungroup Layer
Menu:
"<Image>/Layer/Stack/Ungroup Layer"
"<Layers>/Ungroup Layer"
PDB Name:
script-fu-sg-ungroup-layer
Download:
sg-group-linked-layers.scm (after the page appears, click on the "Download" command)
License:
GPLv2+

Description:

This script adds a command to move a layer out of its containing group, placing it directly above the group's fundament in the layer stack. If the active layer is a fundament, then all of the layers in the group are spliced into the parent group and the fundament is removed from the image.

Note: this command is provided as part of the Group Linked Layers script.