Revert "[Syntax] Use BumpPtrAllocator for Syntax node internals"

[rintaro]

Reverts #2925

This broke macOS package jobs e.g. https://ci.swift.org/job/oss-swift-package-macos/3776/console

error: link command failed with exit code 1 (use -v to see invocation)
ld: warning: ignoring file 'lib/swift/host/lib_SwiftSyntaxCShims.a[2](PlatformMutex.c.o)': found architecture 'x86_64', required architecture 'arm64'
ld: Undefined symbols:
  _swiftsyntax_platform_mutex_create, referenced from:

[rintaro]

@swift-ci Please test

[ahoppen]

@swift-ci Please test Windows