Use model struct as method parameter

[maratori]

Some of insert queries contains all columns of table as input parameters.
In that case generated method may apply model struct instead of ...Params struct.

For example following method
https://github.com/kyleconroy/sqlc/blob/bda1a0089e042a33f64f9dd1b59a2c3631fb659e/examples/ondeck/postgresql/city.sql.go#L28
may easily become

func (q *Queries) CreateCity(ctx context.Context, arg City) (City, error) {

Because table contains two columns
https://github.com/kyleconroy/sqlc/blob/bda1a0089e042a33f64f9dd1b59a2c3631fb659e/examples/ondeck/postgresql/schema/0001_city.sql#L1-L4
and the query uses all of them
https://github.com/kyleconroy/sqlc/blob/bda1a0089e042a33f64f9dd1b59a2c3631fb659e/examples/ondeck/postgresql/query/city.sql#L15-L21

Implementation

For output parameters there is struct "deduplication"
https://github.com/kyleconroy/sqlc/blob/bda1a0089e042a33f64f9dd1b59a2c3631fb659e/internal/codegen/golang/result.go#L183

I believe we need to introduce the same deduplication for input parameters
https://github.com/kyleconroy/sqlc/blob/bda1a0089e042a33f64f9dd1b59a2c3631fb659e/internal/codegen/golang/result.go#L166