chore: remove instrumentation for email performance monitoring and SES migration

[justynoh]

Problem

We created additional instrumentation over our mailing system in #5019 and #5369 and #5442. This PR tears them down, since they are not needed anymore.

Closes https://github.com/opengovsg/formsg-private/issues/130 and closes https://github.com/opengovsg/formsg-private/issues/132.

Cleaning up old SES config will also close https://github.com/opengovsg/formsg-private/issues/91.

Solution

Delete code that references datadog traces and SES in the US.

Breaking Changes

• No - this PR is backwards compatible

Tests

• OTP emails can be sent to admins to log in.
• Email responses can be sent to admins after submitting an email mode form.
• OTP emails can be sent to respondents when verifying an email in a public form.
• Confirmation emails can be sent to respondents when submitting and email mode form.

Deploy Notes

New environment variables:

for x = HOST, PORT, USER, PASS:

• SES_{x} : Should be the value of the old variable SES_{x}_SG
• SES_{x}_US and SES_{x}_SG: Should be deleted

[justynoh]

(This PR must be released before we tear down the infra for SES US)

[timotheeg]

Looking good!

Unless the tracing of the email sending is costing a lot (I assume no right now), let's keep them in for now (traces for email sending + pdf generation), it gives us visibility in processes we are otherwise blind to.

[timotheeg]

is this change intended?

[justynoh]

oops no, but it shouldn't make a difference! it was probably introduced when I reinstated the tracer spans. But it still works, tested on staging + the default import was already used in mail.utils.ts before

[timotheeg]

LGTM