Revert "Set setFailIfPoolExhausted in SessionPoolOptions for SpannerA… #12175

All 4 tests pass in 1h 23m 6s

8 files ±0 8 suites ±0 1h 23m 6s ⏱️ + 4m 47s
4 tests ±0 4 ✅ ±0 0 💤 ±0 0 ❌ ±0
14 runs ±0 14 ✅ ±0 0 💤 ±0 0 ❌ ±0

Results for commit 64854bb. ± Comparison against earlier commit 8eef4a3.