Core SwiftShader should no longer be able to allocate executable
memory. That responsibility now falls entirely on Reactor.

Bug b/115344057
Bug swiftshader:16

Change-Id: If5dad25e52e661331ef0555b2d9de743cbfd3173
Reviewed-on: https://swiftshader-review.googlesource.com/c/21369Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>