Consolidate linux and windows containerd config templates

[brandond]

The containerd config template was split out into separate linux and windows versions in #3411. We're looking at consolidating back to a single unified template for containerd 2.0 in #11626. We should do the same for the containerd 1.7 template.

The separate templates are not necessary, as most of what's in the windows config template is just copy-pasted defaults from a stock containerd config dump that don't need to be explicitly set. There are also some typos in it that are breaking registry auth on windows:

• Windows Node cannot pull images from private registry rancher/rke2#7103 (comment)