Fixes the cache unit tests by removing an undeclared class function, (#8782)

HostStatus::createHostStat(), that was removed with PR #8689.

Author: jrushford

iocore/cache/test/stub.cc

@@ -179,11 +179,6 @@ HostStatus::getHostStatus(const std::string_view name)
   return nullptr;
 }
 
-void
-HostStatus::createHostStat(const std::string_view name, const char *data)
-{
-}
-
 HostStatus::HostStatus() {}
 
 HostStatus::~HostStatus() {}