AWS Lambda: remove no-longer-used options & deprecated function #22252

Remove options and a function in @sentry/aws-serverless that are no longer used but kept for back-compat. (Distinct from #21830 / disableAwsContextPropagation.)

TODOs:

• packages/aws-serverless/src/integration/awslambda.ts:8 — remove this option (no longer used)
• packages/aws-serverless/src/sdk.ts:35 — remove this option (no longer used)
• packages/aws-serverless/src/sdk.ts:65 — remove this function
• packages/aws-serverless/src/sdk.ts:187 — remove the startTrace option (currently set to true only to satisfy the type; has no effect)