With awesome user on @freen
ode, awesome user @utkanos
helped me with ditching /data by making f2fs file system:
1) go to recover (in my case broken TWRP)
2) adb shell (from OS)
3) mkfs.f2fs /dev/block/platform/msm_sdcc.1/by-name/userdata (from OS)
All done. Reboot and you are out of encryption and all user data and apps. Will try to flash stock recovery now.
edit1: tried to flash it with fastboot command but it hanged like in all previous attempts. So I installed OTA even thoug I had philz recovery. The effect was like that that it went to philz recovery and wrote about this signature is not ok.... I taped ignore and it did go to a ahalf of bar progress and then just rebooted and went into system. After couple of seconds it just rebooted and the procedure repeated itself.
edit2: Managed to flash it with mfastboot.exe flash boot boot.img
mfastboot.exe flash recovery recovery.img
FINALYY! And then it installed update properly
176.44.1.en.GB rooted, unlocked