internal: delete unused AlternativeModulePath
internal: delete unused AlternativeModulePath

Change-Id: I599fba23a857861054e7b6683446e6aae4046b1b
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/764169
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite