riscv: remove unused barrier defines

They were introduced in commit fab957c1 ("RISC-V: Atomic and
Locking Code") long after commit 2e39465a ("locking: Remove
deprecated smp_mb__() barriers") removed the remnants of all previous
instances from the tree.
Signed-off-by: Rolf Eike Beer <eb@emlix.com>
[paul.walmsley@sifive.com: stripped spurious mbox header from patch
 description; fixed commit references in patch header]
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>

arch/riscv/include/asm/bitops.h

@@ -23,11 +23,6 @@
 #include <asm/barrier.h>
 #include <asm/bitsperlong.h>
 
-#ifndef smp_mb__before_clear_bit
-#define smp_mb__before_clear_bit()  smp_mb()
-#define smp_mb__after_clear_bit()   smp_mb()
-#endif /* smp_mb__before_clear_bit */
-
 #include <asm-generic/bitops/__ffs.h>
 #include <asm-generic/bitops/ffz.h>
 #include <asm-generic/bitops/fls.h>