scons: Remove "TIMEOUT" variable and checks.
scons: Remove "TIMEOUT" variable and checks.

This was used when regression tests were run from scons. Since that
hasn't been done for a while, these checks and this setting have no
purpose and can be removed.

Change-Id: Ibe383944f1427571061fd25ed6e97d9acfbbc7f1
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40856
Maintainer: Gabe Black <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Andreas Sandberg <c9f5686ee5bd561c93f9de79681eee75bfa7f36e@arm.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5