Revert "mcu/native: Write flash files to macOS TMPDIR"
Revert "mcu/native: Write flash files to macOS TMPDIR"

This reverts commit 16b88cce02b69d538451600117f7013b2990fe82.

This experimental fix did not solve the problem.  Revert it.

mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core