Remove retry routines from mixed_build

The retry routines are added for testing purpose (aosp/730971).
We may now remove this because it has no effect to remove the flaky
build errors.

Bug: 112250435
Test: build_mixed system_dir device_dir out_dir
Change-Id: Ibdefb7da3188ce42b6cd2deb5e40ad777c2fe5b0