dev/sg: fix enterprise-e2e set with env hackery

Created by: bobheadxi

Closes https://github.com/sourcegraph/sourcegraph/pull/38318 and closes https://github.com/sourcegraph/sourcegraph/pull/38319 and uses some env setting in the command itself instead.

Test plan

sg start enterprise-e2e
sg test frontend-e2e

no more extsvc issues