refactor: delete idl dependency and delete unused errors

[stdll00]

Fix these issues:

• case idl.ErrPackageUnselected: case idl.ErrUnknownServiceName: are unreachable.
• Errors in idl package such as ErrPackageUnselected are duplicated with usecase package and it seems seems unused except unreachale case.

Behavior changes

Error message changed when specify service without selecting package or speficy invalid service name.

Prepare

cp repl/testdata/test.proto repl/testdata/test2.proto
sed -i -e 's/package api;/package api2;/g'  repl/testdata/test2.proto # set different package name

On master branch

$ go run main.go --proto repl/testdata/test.proto
...
127.0.0.1:50051> service hoge
command service: unknown service name

$ go run main.go --proto repl/testdata/test.proto --proto repl/testdata/test2.proto
...
127.0.0.1:50051> service api.Example
command service: package unselected

On this branch,

$ go run main.go --proto repl/testdata/test.proto
...
api.Example@127.0.0.1:50051> service hoge
command service: unknown service name 'hoge'

$ go run main.go --proto repl/testdata/test.proto --proto repl/testdata/test2.proto
...
127.0.0.1:50051> service api.Example
command service: package unselected. please execute 'package' command at the first