This reverts commit 2839f76cecb0b5bfc837857d797f090f970c08c5. # Conflicts: # imgui-sys/third-party/cimgui
Use cimgui which avoids the copy-files-into-our-repo step
cimgui has changed a lot, and the default bindings include a lot of internal stuff that we (probably) don't want. Therefore we stop checking out cimgui as a submodule and just use it as a tool instead.