parisc: Remove duplicate struct task_struct declaration

struct task_struct is declared twice. One has been declared
at 154th line. Remove the duplicate.
Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/include/asm/processor.h

@@ -272,7 +272,6 @@ on downward growing arches, it looks like this:
 	regs->gr[23] = 0;				\
 } while(0)
 
-struct task_struct;
 struct mm_struct;
 
 /* Free all resources held by a thread. */