fix: bump to core 3

[WillieRuemmele]

What does this PR do?

bumps to sfdx-core@3
removes unused files
fixes jsdocs
refactors a few unnecessary variables

What issues does this PR fix or reference?

@W-11092409@

[cristiand391]

@WillieRuemmele do you want to release this as minor v3 or as telemetry v4? Make sure to manually bump the version if v4.

[cristiand391]

QA notes:

Checkout salesforcecli/plugin-telemetry#282 and yarn link this PR:

✅ lib respects SFDX_DISABLE_INSIGHTS=true
❌ lib respects disableTelemetry=true setting
❌ when telemetry is disabled, ./bin/run telemetry | sfdx telemetry prints the ID as undefined

With telemetry enabled:

✅ lib respects SFDX_TELEMETRY_DEBUG and can run the uploader manually, also looked at the log and all the event props are properly populated:

✅ lib respects SFDX_TELEMETRY_PATH:

✅ lib respects SFDX_TELEMETRY_DISABLE_ACKNOWLEDGEMENT when the ack file doesn't exists (first run):

[cristiand391]

QA notes:

With oclif/core PR linked

✅ plugin-telemetry respects disableTelemetry setting: