Document is obsolete

[jchimene]

sdks/v2/php/MigrationFromInfusionsoftPhpSdk.md

references non-existent class Keap\KeapClient

[skeemer]

This appears to be a huge indicator of what we should expect from Keap under Thryv. This should have been fixed before they linked the older SDK to this document, let alone not fixed the issue for 6 months.

I'm also guessing that the document is AI slop since someone that actually used the SDK wouldn't randomly add non-existent classes.