x/tools/go/analysis/passes/assign: unsound quickfix (deletes too much)

[adonovan]

The suggested fix reported by the assign analyzer for x = x or x, y = x, 0 deletes the entire statement. That's fine in the first case, but in the second it removes the assignment to y.

The correct fix is to remove only one LHS, RHS pair in the case of a parallel assignment.

Also, it should set Diagnostic.End appropriately.

[gopherbot]

Change https://go.dev/cl/679435 mentions this issue: go/analysis/passes/assign: correctly handle parallel assignments