Revert of Pass --images '' to nanobench to disable image benchmarking. (patchset #1 id:1 of https://codereview.chromium.org/1381703003/ )

Reason for revert:
I have attempted to fix the problems that caused running nanobench with images to fail, so testing to see if they are in fact fixed.

Original issue's description:
> Pass --images '' to nanobench to disable image benchmarking.
>
> Enabling image benchmarking has caused most nanobench runs to fail,
> both Debug and Release.
>
> BUG=skia:3418
> NOTREECHECKS=true
> TBR=scroggo@google.com
>
> Committed: https://skia.googlesource.com/skia/+/1f7039c6c5f0f118b629994b0bac255345e5abd6

BUG=skia:3418

Review URL: https://codereview.chromium.org/1400633002

tools/nanobench_flags.json

@@ -1,6 +1,5 @@
 {
   "Perf-Android-GCC-NexusPlayer-GPU-PowerVR-x86-Release": [
-    "--images", 
     "--scales", 
     "1.0", 
     "1.1", 
@@ -18,7 +17,6 @@
     "~desk_unicodetable"
   ], 
   "Perf-Android-Nexus7-Tegra3-Arm7-Release": [
-    "--images", 
     "--scales", 
     "1.0", 
     "1.1", 
@@ -37,7 +35,6 @@
     "~desk_carsvg"
   ], 
   "Test-Android-GCC-GalaxyS4-GPU-SGX544-Arm7-Release": [
-    "--images", 
     "--scales", 
     "1.0", 
     "1.1", 
@@ -55,7 +52,6 @@
     "~GLInstancedArraysBench"
   ], 
   "Test-Ubuntu-GCC-ShuttleA-GPU-GTX550Ti-x86_64-Release-Valgrind": [
-    "--images", 
     "--scales", 
     "1.0", 
     "1.1", 
@@ -74,7 +70,6 @@
     "1"
   ], 
   "Test-Win7-MSVC-ShuttleA-GPU-HD2000-x86-Debug-ANGLE": [
-    "--images", 
     "--scales", 
     "1.0", 
     "1.1", 
@@ -96,7 +91,6 @@
     "~etc1bitmap"
   ], 
   "Test-iOS-Clang-iPad4-GPU-SGX554-Arm7-Debug": [
-    "--images", 
     "--scales", 
     "1.0", 
     "1.1", 

tools/nanobench_flags.py

@@ -29,9 +29,6 @@ cov_start = lineno()+1   # We care about coverage starting just past this def.
 def get_args(bot):
   args = []
 
-  # Temporarily disable image benchmarking.
-  args.append('--images')
-
   if 'Appurify' not in bot:
     args.extend(['--scales', '1.0', '1.1'])