Remove @method of the qic.mcglm() function

I don't know the reasons, but when `@method` is present
`S3method(residuals,mcglm)` is included in the NAMESPACE and thi error
comes up

Loading mcglm
Error: object 'qic' not found whilst loading namespace 'mcglm'

I think that the `qic` is not considered a generic S3 method by R. So I
kept `qic.mcglm` as a regular function. No problems with building
process where observed.