Please refer screenshot, I installed "Dash to Panel" gnome extension so that my dash and top panel appear in single unit. But the left side default dock is still there. How can I remove the left side dock? Thanks.
Just disable the extension "Ubuntu Dock" in tweak tools.
Probably, in tweak tools, that extension will appear not to be turned on. In that case, click twice on the toggle: once to turn it on and a second time to turn it of again. After that, the dock will be disabled.
If Ubuntu dock in tweak tool is disable and dock is still visible : open dconf editor (install dconf editor : Sudo apt install dconf-tools) now navigate : org->gnome->shell->extensions->dash-to-dock find dock-fixed and change to false
Edit : if you have problem again navigate : org->gnome->shell->extensions->dash-to-dock find intelihide and change to false