Proposal: Drop IMCE upload method

Problem/Motivation

In Drupal 10, IMCE already supports the File module.

Site builders can enable IMCE on the Manage Form Display page, just like for this module:

Content editors can choose IMCE on the node edit page, just like this module:

Given this out-of-the-box support, I propose we remove the IMCE method from this module. It would drastically simplify the code for this module, and focus further development of this feature in the IMCE module instead of splitting that focus.