Revert "lavc/sbrdsp: R-V V neg_odd_64"

While this function can easily be written with vectors, it just fails to
get any performance improvement.

For reference, this is a simpler loop-free implementation that does get
better performance than the current one depending on hardware, but still
more or less the same metrics as the C code:

 func ff_sbr_neg_odd_64_rvv, zve64x
         li      a1, 32
         addi    a0, a0, 7
         li      t0, 8
         vsetvli zero, a1, e8, m2, ta, ma
         li      t1, 0x80
         vlse8.v v8, (a0), t0
         vxor.vx v8, v8, t1
         vsse8.v v8, (a0), t0
         ret
 endfunc

This reverts commit d06fd18f8f.

libavcodec/riscv/sbrdsp_init.c

@@ -26,7 +26,6 @@
 
 void ff_sbr_sum64x5_rvv(float *z);
 float ff_sbr_sum_square_rvv(float (*x)[2], int n);
-void ff_sbr_neg_odd_64_rvv(float *x);
 void ff_sbr_autocorrelate_rvv(const float x[40][2], float phi[3][2][2]);
 void ff_sbr_hf_gen_rvv(float (*X_high)[2], const float (*X_low)[2],
                        const float alpha0[2], const float alpha1[2],
@@ -64,9 +63,5 @@ av_cold void ff_sbrdsp_init_riscv(SBRDSPContext *c)
         }
         c->autocorrelate = ff_sbr_autocorrelate_rvv;
     }
-#if __riscv_xlen >= 64
-    if ((flags & AV_CPU_FLAG_RVV_I64) && (flags & AV_CPU_FLAG_RVB_ADDR))
-        c->neg_odd_64 = ff_sbr_neg_odd_64_rvv;
-#endif
 #endif
 }

libavcodec/riscv/sbrdsp_rvv.S

@@ -68,23 +68,6 @@ NOHWF   fmv.x.w  a0, fa0
         ret
 endfunc
 
-#if __riscv_xlen >= 64
-func ff_sbr_neg_odd_64_rvv, zve64x
-        li      a1, 32
-        li      t1, 1 << 63
-1:
-        vsetvli t0, a1, e64, m8, ta, ma
-        vle64.v v8, (a0)
-        sub     a1, a1, t0
-        vxor.vx v8, v8, t1
-        vse64.v v8, (a0)
-        sh3add  a0, t0, a0
-        bnez    t0, 1b
-
-        ret
-endfunc
-#endif
-
 func ff_sbr_autocorrelate_rvv, zve32f
         vsetvli t0, zero, e32, m4, ta, ma
         vmv.v.x v0, zero