Remove hard-coded AWS partitions

[maafk]

Also removing unused method that had hard-coded partition inside

What did you implement

• Removed some hard-coded aws partitions to account for non-standard partitions such as aws-cn or aws-us-gov
• Removed unused method that included a hard-coded partition

How can we verify it

Tricky to verify since would need an AWS account than can select gov-cloud or China regions, but deploy a function with ALB as event source in a gov-cloud or China region.

service: my-gov-cloud-app

provider:
  name: aws
  runtime: python3.6
  region: us-gov-west-1  # gov-cloud region

functions:
  albEventConsumer:
    handler: handler.hello
    events:
      - alb:
          # notice the partition in the ARN
          listenerArn: arn:aws-us-gov:elasticloadbalancing:us-east-1:12345:listener/app/my-load-balancer/50dc6c495c0c9188/
          priority: 1
          conditions:
            path: /hello
  myLambdaAtEdge:
    handler: myLambdaAtEdge.handler
    events:
      - cloudFront:  # not currently possible in gov-cloud, but may be soon
          eventType: viewer-response
          origin: s3://bucketname.s3.us-gov-west-1.amazonaws.com/files

Note Cloudfront isn't available for govcloud regions, but is available in China

Todos

Useful Scripts

• npm run test:ci --> Run all validation checks on proposed changes
• npm run lint:updated --> Lint all the updated files
• npm run lint:fix --> Automatically fix lint problems (if possible)
• npm run prettier-check:updated --> Check if updated files adhere to Prettier config
• npm run prettify:updated --> Prettify all the updated files

• Write and run all tests
• Write documentation
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: YES
Is it a breaking change?: NO

[codecov-io]

Codecov Report

Merging #7175 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #7175      +/-   ##
==========================================
+ Coverage   87.94%   87.99%   +0.05%     
==========================================
  Files         236      236              
  Lines        8611     8606       -5     
==========================================
  Hits         7573     7573              
+ Misses       1038     1033       -5

Impacted Files	Coverage Δ
...ins/aws/package/compile/events/cloudFront/index.js	89.83% <ø> (ø)	⬆️
lib/plugins/aws/provider/awsProvider.js	92.85% <ø> (+1.91%)	⬆️
...aws/package/compile/events/websockets/lib/stage.js	100% <ø> (ø)	⬆️
...ins/aws/package/compile/events/alb/lib/validate.js	97.26% <100%> (ø)	⬆️

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[medikoo]

Looks great @maafk Thank you!