at_commons: deprecate apkam value in enum PkamAuthMode

[murali-shris]

Describe the bug

• PkamAuthMode apkam was initially created under the assumption that this flag will be used during onboarding/auth
• Deprecate this value since it is not used

Steps to reproduce

n/a

Expected behavior

n/a

Screenshots

No response

Smartphones

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Were you using an atApplication when the bug was found?

No response

Additional context

No response

[murali-shris]

Fixed https://github.com/atsign-foundation/at_libraries/pull/579