refactor: nix unused low-level resend func

The comment indicates this isn't used anywhere else.
There are no uses of it in our codebase.

Author: nams1570

apps/backend/src/lib/emails-low-level.tsx

@@ -10,8 +10,6 @@ import { runAsynchronously, wait } from '@stackframe/stack-shared/dist/utils/pro
 import { Result } from '@stackframe/stack-shared/dist/utils/results';
 import { traceSpan } from '@stackframe/stack-shared/dist/utils/telemetry';
 import nodemailer from 'nodemailer';
-import { Resend } from 'resend';
-import { getTenancy } from './tenancies';
 
 export function isSecureEmailPort(port: number | string) {
   let parsedPort = parseInt(port.toString());
@@ -221,42 +219,3 @@ export async function lowLevelSendEmailDirectWithoutRetries(options: LowLevelSen
 
   return result;
 }
-
-// currently unused, although in the future we may want to use this to minimize the number of requests to Resend
-export async function lowLevelSendEmailResendBatchedDirect(resendApiKey: string, emailOptions: LowLevelSendEmailOptions[]) {
-  if (emailOptions.length === 0) {
-    return Result.ok([]);
-  }
-  if (emailOptions.length > 100) {
-    throw new StackAssertionError("sendEmailResendBatchedDirect expects at most 100 emails to be sent at once", { emailOptions });
-  }
-  if (emailOptions.some(option => option.tenancyId !== emailOptions[0].tenancyId)) {
-    throw new StackAssertionError("sendEmailResendBatchedDirect expects all emails to be sent from the same tenancy", { emailOptions });
-  }
-  const tenancy = await getTenancy(emailOptions[0].tenancyId);
-  if (!tenancy) {
-    throw new StackAssertionError("Tenancy not found");
-  }
-  const resend = new Resend(resendApiKey);
-  const result = await Result.retry(async (_) => {
-    const { data, error } = await resend.batch.send(emailOptions.map((option) => ({
-      from: option.emailConfig.senderEmail,
-      to: option.to,
-      subject: option.subject,
-      html: option.html ?? "",
-      text: option.text,
-    })));
-
-    if (data) {
-      return Result.ok(data.data);
-    }
-    if (error.name === "rate_limit_exceeded" || error.name === "internal_server_error") {
-      // these are the errors we want to retry
-      return Result.error(error);
-    }
-    throw new StackAssertionError("Failed to send email with Resend", { error });
-  }, 3, { exponentialDelayBase: 2000 });
-
-  return result;
-}
-