fmt: fix removal of used selective and alias imports in modules in $VMODULES dirs

[ttytm]

Fixes issues the formatter introduces(/false negative formatting checks) in modules that are located in a $VMODULES directory.

E.g. the following, when located in ~/.vmodules,...

// ~/.vmodules/foo/main.v
import x.json2 as json
import datatypes { Stack }

const my_datatype = Stack[string]{}

will currently be formatted into:

// ~/.vmodules/foo/main.v
import x.json2
import datatypes

const my_datatype = Stack[string]{}

[spytheman]

Excellent work.