Remove the sleep throttle applied in 10625 to work around an Intel GPU driver
bug. It was erroneously being applied to all GPUs, and also as of Intel driver
26.20.100.7755 (1/9/2020) it appears that the driver bug no longer exists.

following promotion of DRTVWR-501

to reflect previous commit and use correct pool size

following promotion of DRTVWR-476

This reverts commit bf999f2f due to revert of updater, this will be moved to separate 'epic' instead

This fails at teamcity due to missing LLTrans, but builds locally without issues. Reverting to not hold D501

This reverts commit 31d9930a.

LLExtStat had been a S32, this wasn't right, as some of the constants lead to integer overflow: const LLExtStat LL_EXSTAT_RES_RESULT = 2L<<30; const LLExtStat LL_EXSTAT_VFS_RESULT = 3L<<30; This shifts into the sign bit and clang gets (rightfully) upset about this.

LLExtStatus needs to be at least of type U32 to remedy this problem, but
while at it it makes sense to turn it into what it is: An enum. Turning
it into a class enum has the added benefit we get type safety for mostly
free.
Which incidentally turned up a problem right away:
A call to removeAndCallbackPendingDownloads had status and extstatus
reversed and thus was wrong.

following promotion of DRTVWR-476