Remove field_ui_theme_suggestions_form_element_alter in favor of specifying the theme wrapper on the element

Problem/Motivation

#3356894: Make field selection less overwhelming by introducing groups added a new theme suggestions hook field_ui_theme_suggestions_form_element_alter but we could just specify the wrapper at the source

Additionally, we're switching out a theme hook for a base hook but changing from 'render elements' to 'variables' which technically isn't supported.

Steps to reproduce

Proposed resolution

Specify the wrapper at the source instead
Switch back to 'render elements' instead of 'variables'

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet