powerpc: Remove unneeded inline functions

Both of those functions are only called from 64-bit only code, so the
stubs should not be needed at all.
Suggested-by: NMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NYueHaibing <yuehaibing@huawei.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200717112714.19304-1-yuehaibing@huawei.com

arch/powerpc/include/asm/mmu_context.h

@@ -218,8 +218,6 @@ static inline void inc_mm_active_cpus(struct mm_struct *mm) { }
 static inline void dec_mm_active_cpus(struct mm_struct *mm) { }
 static inline void mm_context_add_copro(struct mm_struct *mm) { }
 static inline void mm_context_remove_copro(struct mm_struct *mm) { }
-static inline void mm_context_add_vas_windows(struct mm_struct *mm) { }
-static inline void mm_context_remove_vas_windows(struct mm_struct *mm) { }
 #endif