eclass/go-module: remove go-get for corner case of unneeded deep build dependencies

eclass/go-module: remove go-get for corner case of unneeded deep build dependencies

The helper function used to call 'go get' to verify by fake-fetching everything
from the main go.mod. However 'go get' also turns out to recursively try to
fetch everything in dependencies, even materials that are used only for tests
of the dependencies, or code generation.

If EGO_SUM is missing an entry now, it will fail during the build process
rather than the helper function.

Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>