remove az for pending major release

[bwagner5]

Issue #, if available:
N/A

Description of changes:

• The singular AZ param was deprecated previously, but since we are pending a major release to include the ByteQuantity changes, we can remove the singular AZ handling in favor of the plural --availability-zones param.

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.61%. Comparing base (acdbb43) to head (cd47c72).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #42      +/-   ##
==========================================
+ Coverage   88.38%   88.61%   +0.22%     
==========================================
  Files           9        9              
  Lines        1068     1063       -5     
==========================================
- Hits          944      942       -2     
+ Misses         88       87       -1     
+ Partials       36       34       -2     

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[brycahta]

Couple other places:

• amazon-ec2-instance-selector/pkg/selector/types.go

  Line 101 in 2433734

  // AvailabilityZone [DEPRECATED] is the AWS Availability Zone where instances will be provisioned.

• amazon-ec2-instance-selector/pkg/selector/selector.go

  Line 146 in a67979b

  // Support the deprecated singular availabilityZone filter in favor of the plural

[bwagner5]

good catch once again! fixed

[brycahta]

Looks good! 👍🏼

pumped for the 2.0 launch party 🎉