Update Taskfile contribution guidelines to use utility tasks in yscope-dev-utils.

[kirkrodrigues]

Description

y-scope/yscope-dev-utils#2 added taskfiles containing the checksuming utility tasks listed in the Taskfile contribution guidelines. Thus, we can now remove them from the contribution guidelines and update the example to use the utility tasks in yscope-dev-utils directly.

[haiqi96]

After carefully reading the previous version of doc, I finally understands why we need the generates for the checksum.

So yeah, I didn;t read the doc carefully and wasn't awared that validate-checksum will delete the checksum file if validation has failed. Basically, I mis-interpreted deps as something similar to makefile, i.e. if something has changed in deps then the task target will rerun. So i was thinking the target will rerun if validate-checksum fails and we don't really need the generates for checksum.

Since now we are removing the implementation details of validate-checksum from the doc and link it, lazy programmers like me are very unlikely to read the original implementation of validate-checksum carefully.

I think it might be better to either

1. Emphasize somewhere in the doc that validate-checksum actually deletes the checksum file.
2. Rename validate-checksum to something like validate-or-remove-checksum