After CL 104636 the feature flags in internal/cpu are initialized before
alginit and can now be used for aeshash feature detection. Also remove
now unused runtime variables:
x86:
	support_ssse3
	support_sse42
	support_aes
arm64:
	support_aes

Change-Id: I2f64198d91750eaf3c6cf2aac6e9e17615811ec8
Reviewed-on: https://go-review.googlesource.com/106015
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>