rts: drop unused 'SpinLockCount' typedef

Summary: Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

Test Plan: git grep, git log -SSpinLockCount, build test

Reviewers: austin, simonmar

Reviewed By: austin, simonmar

Subscribers: phaskell, simonmar, relrod, carter

Differential Revision: https://phabricator.haskell.org/D76

includes/rts/SpinLock.h

@@ -34,8 +34,6 @@ typedef struct SpinLock_
 typedef StgWord SpinLock;
 #endif
 
-typedef StgWord SpinLockCount;
-
 #if defined(PROF_SPIN)
 
 // PROF_SPIN enables counting the number of times we spin on a lock