chore(ios)!: remove unused & deprecated code & styling formatting

[erisu]

Description

• Remove unused methods & properties/variables
• Remove some of the deprecated code/defines/protocols of GCM
  • This PR does not rename of variables
• Remove excessive newlines
• Cleanup formatting

Note: The fcmSandbox is an iOS option that replaced gcmSandbox in version 2.0.0 of the phonegap-push-plugin days, but when GCM was dropped, fcmSandbox did not actual configure anything. This option can be dropped since it was never used and also FCM automatically determines the environment type.

Related Issue

N/A

Motivation and Context

Cleanup code base

How Has This Been Tested?

• Build and run app in simulator.

Screenshots (if appropriate):

Types of changes

• Refactor/Chore (non-breaking change, non-functionality change)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[github-actions]

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