Don't stub Rakudo::Internals::HyperWorkBatch

Removing this line unbreaks the build on the JVM backend.
It seems to be not necessary for MoarVM, cmp.
https://colabti.org/irclogger/irclogger_log/perl6-dev?date=2019-08-19#l32

src/core/core_prologue.pm6

@@ -10,7 +10,6 @@ my class Rakudo::Deprecations { ... }
 my class Rakudo::Internals { ... }
 my class Rakudo::Internals::JSON { ... }
 my class Rakudo::Internals::RegexBoolification6cMarker { ... }
-my class Rakudo::Internals::HyperWorkBatch { ... }
 my class Rakudo::Iterator { ... }
 #?if !js
 my class ThreadPoolScheduler { ... }