Remove --tmpdir from mktemp

This option is not portable and does not work on Darwin. The -t option
and the usage of a relative name implies anyway that $TMPDIR will be
used, on all mktemp versions.

Change-Id: I3abfc8606b37d6e2f8c5ff4dc6855a4558e8f7c9
Merge "Remove --tmpdir from mktemp"