compiler.h: remove GCC < 3 __builtin_expect fallback

Since commit efc6c07 ("configure: Add a test for the minimum compiler
version"), QEMU explicitely depends on GCC >= 4.8.

(clang >= 3.4 advertizes itself as GCC >= 4.2 compatible and supports
__builtin_expect too)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20201210134752.780923-4-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/qemu/compiler.h

@@ -44,10 +44,6 @@
 #endif
 
 #ifndef likely
-#if __GNUC__ < 3
-#define __builtin_expect(x, n) (x)
-#endif
-
 #define likely(x)   __builtin_expect(!!(x), 1)
 #define unlikely(x)   __builtin_expect(!!(x), 0)
 #endif