After some testing with Linux I figured I didn’t need it on this machine. As a 128GB SSD is not that gigantic I wanted to reclaim the diskspace it used.
The configuration was pretty basic: 2 partitions for Windows 8.1 (350MB system reserved partition and a large Windows partition) and 2 partitions for Linux (swap and ext4). Simply deleting the Linux partition rendered the system to an unbootable state. After resizing the Windows partition again and reinstalling Linux the system booted again.
Some time later I continued my quest for disk space reclaiming. Basically I used the procedure on techmesto.com.
To be a little more on the safe time now I removed GRUB2 first: I booted from my Windows 8.1 USB install disk. When the first dialog came up (language selection) I pressed Shift-F10 to open a Cmd prompt. I ran the “bootrec.exe /fixmbr” command and after reboot GRUB2 was indeed gone.
I deleted the Linux partitions with the Windows Disk Management. Then I booted from a Linux Live USB disk and increased the Windows partition size again with GParted.