Revert "Add a lock to PlatformPOSIX::DoLoadImage"
Revert "Add a lock to PlatformPOSIX::DoLoadImage"

This reverts commit 1adab33f20e6c7ef7f4914e94ed7c47ae85552e2.

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb