Remove length arg from transmit() in IR HAL

The length argument is not necessary since the pattern is
passed to transmit() as a hidl_vec, so remove it.

Test: Built and called new transmit() function.
Change-Id: I4bee4557c2cca6562a43df5e22a7d6b846f20bb4
Signed-off-by: Connor O'Brien <connoro@google.com>