Correct parameters used with default (hosted) pools

[dougbu]

The AzDO pipeline change @MattGal made in aspnet/Extensions@d4522c6b2e should work short term. But, the future-proof way to do this is to specify just the vmImage and not the pool name when using the default (hosted) pools e.g.

pool:
  vmImage: ubuntu-16.04

instead of

pool:
  name: Hosted Ubuntu 1604
  vmImage: ubuntu-16.04

Background is AzDO is merging their various pools into one and deprecating the name parameter when using these pools (soon to be "this pool").

We need to do this across our repos, including release/2.x branches:

• [x] aspnet/AspLabs / master
• [x] aspnet/AspNetCore / release/2.1
• [x] aspnet/AspNetCore / release/2.2
• [x] aspnet/AspNetCore / master
• [x] aspnet/AspNetCore-Tooling / master
• [x] aspnet/BuildTools / release/2.1
• [x] aspnet/BuildTools / release/2.2
• [x] aspnet/BuildTools / master
• [x] aspnet/EntityFrameworkCore / release/2.1
• [x] aspnet/EntityFrameworkCore / release/2.2
• [x] aspnet/EntityFrameworkCore / master
• [x] aspnet/Extensions / release/2.1
• [x] aspnet/Extensions / release/2.2
• [x] aspnet/Extensions / master

[dougbu]

Where necessary i.e. when we've hit resource limits using the default (hosted) pools in release/2.x branches, move to using BYOC pools (see also aspnet/AspNetCore-Internal#2033).

In addition, use this opportunity to clean up any references to the following deprecated pools.

• dnceng-linux-external-temp
• dnceng-linux-internal-temp
• dnceng-windows-spanish-external-temp
• dotnet-external-temp
• dotnet-external-temp-vs2017
• dotnet-external-temp-vs2019
• dotnet-internal-temp
• dotnet-internal-temp-vs2019

[dougbu]

We also have AzDO YAML files using the old "phase" schema that AzDO has deprecated. Should move to current "job" schema. See https://github.com/dotnet/arcade/blob/master/Documentation/AzureDevOps/PhaseToJobSchemaChange.md

[dougbu]

Done everywhere