These structures were zero-initialized to work around MSan false-
positives. Now that Reactor routines can be instrumented, we can omit
the initialization and detect whether they are properly set by the
normal code paths.

Bug: b/155148722
Change-Id: Ic1136f08b5203531ffc2eda15e7d64d7c2a0d8c5
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/49890
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>