Revert "mkvmuxer,Cluster::Size: make uint64 conversion explicit"

This reverts commit 46b20057cfc24437fbe8987e0b70e0c4c8ecac75.

The conversion results in a warning with Xcode. The original code was
correct given mkvmuxer::uint64 is defined as unsigned long long

Change-Id: I0e5a45c1df85ca59267ab444b386e44442a099ef
1 file changed