core-services/prow/02_config: Drop eastus1 from Azure

Maybe this is the wrong name?  We're seeing [1]:

  level=info msg=Credentials loaded from file "/var/run/secrets/ci.openshift.io/cluster-profile/osServicePrincipal.json"
  level=fatal msg=failed to fetch Master Machines: failed to load asset "Install Config": [platform.azure.region: Invalid value: "eastus1": region "eastus1" is not valid or not available for this account, compute[0].platform.azure.type: Invalid value: "Standard_D4s_v3": not found in region eastus1]

but only from eastus1.  And before 7aa198b
(ci-operator/step-registry/ipi/conf/azure: Region from Boskos lease,
2020-10-14, openshift#12584), which landed last night, we weren't using
useast1.

[1]: openshift#12584 (comment)

core-services/prow/02_config/_boskos.yaml

@@ -220,16 +220,6 @@ resources:
  - centralus--13
  - centralus--14
  - centralus--15
- - eastus1--0
- - eastus1--1
- - eastus1--2
- - eastus1--3
- - eastus1--4
- - eastus1--5
- - eastus1--6
- - eastus1--7
- - eastus1--8
- - eastus1--9
  - eastus2--0
  - eastus2--1
  - eastus2--2

core-services/prow/02_config/generate-boskos.py

@@ -16,7 +16,6 @@
  # and each cluster needs three of public IPs: https://docs.openshift.com/container-platform/4.5/installing/installing_azure/installing-azure-account.html#installation-azure-limits_installing-azure-account
  'centralus': 16,
  # Wild guesses. We'll see when we hit quota issues
- 'eastus1': 10,
  'eastus2': 10,
  'westus': 10
  },