sha3: remove go:nocheckptr annotation

As of Go 1.14.1, -d=checkptr no longer errors on unaligned reads of
non-pointer data.

This reverts the code change (but not the test) from CL 222855.

Fixes golang/go#37644
Updates golang/go#37298

Change-Id: I935c773a3541ed8dca7eb005d39a082eb5f10eb8
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/249378
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

sha3/xor_unaligned.go

@@ -16,15 +16,6 @@ func (b *storageBuf) asBytes() *[maxRate]byte {
 	return (*[maxRate]byte)(unsafe.Pointer(b))
 }
 
-//go:nocheckptr
-//
-// xorInUnaligned intentionally reads the input buffer as an unaligned slice of
-// integers. The language spec is not clear on whether that is allowed.
-// See:
-// 	https://golang.org/issue/37644
-// 	https://golang.org/issue/37298
-// 	https://golang.org/issue/35381
-
 // xorInUnaligned uses unaligned reads and writes to update d.a to contain d.a
 // XOR buf.
 func xorInUnaligned(d *state, buf []byte) {