collapse parametric_{r,g,b} into parametric, remove _a and gamma_dst

parametric_a and gamma_dst were unused outside of unit tests.

In all other cases, we always use parametric_{r,g,b} together
and always pass them the same argument.  So we can collapse
them into a single stage like gamma and to/from_srgb.

Change-Id: I08cea896c7744f97b4f4bf9e029f5d643e45e177
Reviewed-on: https://skia-review.googlesource.com/140576
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Brian Osman <brianosman@google.com>
diff --git a/bench/SkRasterPipelineBench.cpp b/bench/SkRasterPipelineBench.cpp
index 5ddf43d..6dd7415 100644
--- a/bench/SkRasterPipelineBench.cpp
+++ b/bench/SkRasterPipelineBench.cpp
@@ -130,12 +130,8 @@
         SkRasterPipeline p(&alloc);
         p.append_constant_color(&alloc, c);
         if (fParametric) {
-            p.append(SkRasterPipeline::parametric_r, &from_2dot2);
-            p.append(SkRasterPipeline::parametric_g, &from_2dot2);
-            p.append(SkRasterPipeline::parametric_b, &from_2dot2);
-            p.append(SkRasterPipeline::parametric_r, &  to_2dot2);
-            p.append(SkRasterPipeline::parametric_g, &  to_2dot2);
-            p.append(SkRasterPipeline::parametric_b, &  to_2dot2);
+            p.append(SkRasterPipeline::parametric, &from_2dot2);
+            p.append(SkRasterPipeline::parametric, &  to_2dot2);
         } else {
             p.append(SkRasterPipeline::gamma, &from_2dot2.fG);
             p.append(SkRasterPipeline::gamma, &  to_2dot2.fG);