Docker compose: remove host network requirement when building

This PR fixes the following issue when running docker-compose:

    failed to solve: granting entitlement network.host is not allowed by build daemon configuration

Using the host network is not required anyway, as the build is able to finish without it.

docker-compose.yml

@@ -18,7 +18,6 @@ services:
  polaris:
  build:
  context: .
- network: host
  ports:
  - "8181:8181"
  - "8182"
@@ -47,7 +46,6 @@ services:
  regtest:
  build:
  context: regtests
- network: host
  args:
  POLARIS_HOST: polaris
  depends_on: