fix: remove stale preflightCommitment workaround in sendEncodedTransaction

[babuClawd]

Summary

Removes a stale workaround in sendEncodedTransaction() that was added to work around a validator bug.

Closes #3733

Background

In sendEncodedTransaction(), there was a FIXME comment explaining that preflightCommitment was hardcoded to 'processed' when skipPreflight === true:

// Before
const preflightCommitment =
  skipPreflight === true
    ? 'processed' // FIXME Remove when https://github.com/anza-xyz/agave/pull/483 is deployed.
    : (options && options.preflightCommitment) || this.commitment;

This workaround was added to work around a bug in the Agave validator where skipping preflight with non-processed commitment could cause issues with last_valid_block_height calculation.

Why It's Safe to Remove

anza-xyz/agave#483 was merged on 2024-04-03 — almost 2 years ago. The fix has been deployed to mainnet validators for well over a year.

Change

// After
const preflightCommitment =
  (options && options.preflightCommitment) || this.commitment;

preflightCommitment now behaves consistently regardless of skipPreflight:

• Uses options.preflightCommitment if explicitly provided
• Falls back to connection.commitment

Impact

Behavior change: When skipPreflight: true and no explicit preflightCommitment is passed, the value sent to the RPC changes from hardcoded 'processed' to the connection's configured commitment level (typically 'finalized' on mainnet).

Risk: Low — the workaround's target bug has been fixed at the validator level. The RPC parameter is now passed correctly per user intent.

Testing

No new test needed — this is a logic simplification in an existing code path. Existing tests cover sendEncodedTransaction() behavior.