[REF] survey: remove dead or duplicated code

PURPOSE

Purpose is to perform some cleaning in survey models: naming, ordering,
dead code [0]. As new features are about to land in survey, notably live
interactions [1] and new survey building [2] performing a pre cleaning
is necessary [3].

SPECIFICATIONS

Remove dead code :

  * old code bits not used anymore since several code cleanings have
    already been performed;
  * use tools when possible instead of manually checking stuff like
    email validation;
  * clean unused imports;

No functional changes should occur with this commit. It contains only
code move, not any change at all.

LINKS

[0] Related to Task ID 2144393 (surveys split / cleaning)
[1] Task ID 1972640 (live interactions)
[2] Task ID 2119587 (new frontend for building surveys)
[3] Task ID 2061901 (survey models cleaning and preparation)

PR #40623

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