Disable rect_tx because we only support 4x4 Walsh-Hadamard transform
in lossless mode.

Fixes failure in ./test_libaom --gtest_filter=*Large*ScreencastQ0/1
Configuration: --enable-experimental --enable-var-tx --enable-rect-tx
 --enable-ref-mv --enable-ext_intra --enable-ext_tx --enable-debug
 --disable-optimizations

Change-Id: Ib6b3494c7dcf7182f1cab9b138388d054851a23d