get_tx_type: remove dead store
get_tx_type: remove dead store

w/ !(FIXED_TX_TYPE || CONFIG_EXT_TX)

BUG=aomedia:445

Change-Id: I4e9e531f1983656030c61d823e16f7704b89cfdd

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom