feat!: remove built-ins polyfills on node >= 18 #59

Job	Run time
ʦ TypeScript (form-data)	24s
ʦ TypeScript (file)	24s
ʦ TypeScript (fetch)	24s
🧪 Test (fetch / ubuntu-latest / node@18)	32s
🧪 Test (form-data / ubuntu-latest / node@18)	31s
🧪 Test (file / ubuntu-latest / node@18)	32s
🧪 Test (fetch / windows-latest / node@18)	4m 32s
🧪 Test (file / macos-latest / node@18)	30s
🧪 Test (form-data / windows-latest / node@18)	2m 32s
🧪 Test (file / ubuntu-latest / node@20)	30s
🧪 Test (fetch / macos-latest / node@18)	38s
🧪 Test (form-data / ubuntu-latest / node@20)	41s
🧪 Test (file / macos-latest / node@20)	27s
🧪 Test (fetch / windows-latest / node@20)	2m 1s
🧪 Test (form-data / macos-latest / node@20)	25s
🧪 Test (form-data / macos-latest / node@18)	28s
🧪 Test (form-data / windows-latest / node@20)	3m 13s
🧪 Test (fetch / ubuntu-latest / node@20)	26s
🧪 Test (file / windows-latest / node@18)	4m 53s
🧪 Test (fetch / macos-latest / node@20)	26s
🧪 Test (file / windows-latest / node@20)	3m 11s
	27m 40s

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