perf: use IDBObjectStore.clear

[nolanlawson]

There's no need to do separate objectStore.delete()s when we can just call objectStore.clear().

[github-actions]

📊 Tachometer Benchmark Results

Summary

benchmark-total

• emoji-picker-element-first-load: unsure 🔍 -7% - +7% (-4.90ms - +5.36ms)
  ^{this-change vs tip-of-tree}
• emoji-picker-element-second-load: unsure 🔍 -7% - +9% (-5.55ms - +6.64ms)
  ^{this-change vs tip-of-tree}

Results

emoji-picker-element-first-load

• Browser: chrome-headless 92.0.4515.131
• Sample size: 50
• Built by: Benchmarks #85

• Commit: ea36243

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree
this-change	69.30ms - 76.49ms	-	unsure 🔍 -7% - +7% -4.90ms - +5.36ms
tip-of-tree tip-of-tree	69.01ms - 76.32ms	unsure 🔍 -7% - +7% -5.36ms - +4.90ms	-

emoji-picker-element-second-load

• Browser: chrome-headless 92.0.4515.131
• Sample size: 50
• Built by: Benchmarks #85

• Commit: ea36243

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree
this-change	70.60ms - 79.02ms	-	unsure 🔍 -7% - +9% -5.55ms - +6.64ms
tip-of-tree tip-of-tree	69.86ms - 78.67ms	unsure 🔍 -9% - +7% -6.64ms - +5.55ms	-

_{tachometer-reporter-action v2 for Benchmarks}

[github-actions]

Size Change: -61 B (0%)

Total Size: 41.5 kB

Filename	Size	Change
./bundle.js	41.5 kB	-61 B (0%)

_{compressed-size-action}