Speed up tune=vmaf_with_preprocessing mode

Disable RDO multiplier scaling for this mode to save encoding time.
The mode differences can be summarized as following:
                           tune=vmaf   vmaf_with_pp   vmaf_without_pp
Frame based preprocessing      X             V               X
Block based preprocessing      V             X               X
RDO multiplier scaling         V             X               V
QP adjustment                  V             V               V

The VMAF BD-rate change
-----------------------
Baseline: tune=psnr
                old       new
Lowres_10bd   -25.88%   -25.44%
Midres        -27.18%   -25.50%
Midres_10bd   -30.73%   -30.90%
Hdres         -36.72%   -36.03%

Fyi,
             tune=vmaf    vmaf_without_preprocessing
Lowres_10bd   -26.90%               -5.06%
Midres        -28.19%               -4.77%
Midres_10bd   -33.10%               -4.24%
Hdres         -38.04%               -4.59%

Speed test for different modes
------------------------------
Performance counter stats for './aomenc red_kayak_480p.y4m --limit=30
 -o output_new --tune=vmaf_without_preprocessing --cpu-used=1'
New tune=vmaf_with_preprocessing
   774,724,635,890      instructions:u
     104.010053526 seconds time elapsed
     104.012937000 seconds user
       3.858861000 seconds sys

Old tune=vmaf_with_preprocessing
 1,310,749,642,864      instructions:u
      93.577722852 seconds time elapsed
     226.912579000 seconds user
       5.209748000 seconds sys

Fyi,
Tune=psnr
   649,048,190,935      instructions:u
      84.420997459 seconds time elapsed
      84.107771000 seconds user
       0.303984000 seconds sys

Tune=vmaf
 1,412,870,451,983      instructions:u
     153.464040921 seconds time elapsed
     262.993312000 seconds user
      81.008326000 seconds sys

Tune=vmaf_without_preprocessing
 1,230,166,789,702      instructions:u
      83.081840326 seconds time elapsed
     206.672262000 seconds user
       6.002862000 seconds sys

Change-Id: Idf3808ec5926a1d7c9b793459198640cb023f497
diff --git a/av1/encoder/encodeframe.c b/av1/encoder/encodeframe.c
index 1e4b9a2..40eeb6a 100644
--- a/av1/encoder/encodeframe.c
+++ b/av1/encoder/encodeframe.c
@@ -375,8 +375,7 @@
     set_ssim_rdmult(cpi, x, bsize, mi_row, mi_col, &x->rdmult);
   }
 #if CONFIG_TUNE_VMAF
-  if (cpi->oxcf.tuning == AOM_TUNE_VMAF_WITH_PREPROCESSING ||
-      cpi->oxcf.tuning == AOM_TUNE_VMAF_WITHOUT_PREPROCESSING ||
+  if (cpi->oxcf.tuning == AOM_TUNE_VMAF_WITHOUT_PREPROCESSING ||
       cpi->oxcf.tuning == AOM_TUNE_VMAF_MAX_GAIN) {
     av1_set_vmaf_rdmult(cpi, x, bsize, mi_row, mi_col, &x->rdmult);
   }
diff --git a/av1/encoder/encoder.c b/av1/encoder/encoder.c
index 751e0dd..c58215e 100644
--- a/av1/encoder/encoder.c
+++ b/av1/encoder/encoder.c
@@ -6307,7 +6307,6 @@
 
 #if CONFIG_TUNE_VMAF
   if (oxcf->tuning == AOM_TUNE_VMAF_WITHOUT_PREPROCESSING ||
-      oxcf->tuning == AOM_TUNE_VMAF_WITH_PREPROCESSING ||
       oxcf->tuning == AOM_TUNE_VMAF_MAX_GAIN) {
     av1_set_mb_vmaf_rdmult_scaling(cpi);
   }