[infra] Migrate android-nougat-x86-rel from Ninja to Siso

The experimental android-nougat-x86-siso-rel satisfies the rollout criteria as follows.

# Build speed
- P90: +44% speed up (11.73m -> 8.15m)
- P50: +14% speed up (6.68 -> 5.87m)

Data: http://screen/8pMb49kxfi5zXre

# Build failures
- No failure rate increase observed (9% -> 8%)
- No infra failure rate increase observed (0% -> 0%)

Data: http://screen/9KCjx92QVmAmkbt

Bug: b/277863839
Change-Id: I94a7b83f5fbc98dded0a76ecf2a45b140e715949
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4876141
Auto-Submit: Junji Watanabe <jwata@google.com>
Reviewed-by: Struan Shrimpton <sshrimp@google.com>
Commit-Queue: Struan Shrimpton <sshrimp@google.com>
Cr-Commit-Position: refs/heads/main@{#1198619}