revert(secret): remove versioned AES-GCM format from main

[alexey-igrychev]

Summary

Revert #35 from main. The secret-format change was intended for the 1 release branch, so main must return to its pre-#35 behavior before it reaches a release.

What

• main no longer writes the AES-GCM secret formats or changes YAML scalar encryption behavior introduced by feat(secret): add versioned AES-GCM format and YAML scalar fidelity #35.
• main source matches commit 0558f83edc6de3c23b13c37e2728e01141f93282, the commit immediately before feat(secret): add versioned AES-GCM format and YAML scalar fidelity #35.
• The reviewed change remains prepared locally for a separate PR targeting branch 1; this revert does not alter that release-branch work.

Why

#35 was merged into the wrong target branch. Reverting through a PR preserves public history and prevents the new secret format from shipping from main while the intended v1 backport is prepared.

[alexey-igrychev]

Verification

• task test:unit passed locally.
• The complete tree diff from 0558f83edc6de3c23b13c37e2728e01141f93282 to this revert commit is empty.

Follow-up

• Open the reviewed secret-format change against https://github.com/werf/common-go/tree/1 after this revert lands.