remove alphatype from colortable

the owning bitmap is (already) responsible for knowing the alphatype

BUG=skia:
R=djsollen@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/611093002
diff --git a/samplecode/SampleDitherBitmap.cpp b/samplecode/SampleDitherBitmap.cpp
index e05d074..d825c71 100644
--- a/samplecode/SampleDitherBitmap.cpp
+++ b/samplecode/SampleDitherBitmap.cpp
@@ -57,11 +57,10 @@
     for (int i = 0; i < 256; i++) {
         c[i] = SkPackARGB32(0xFF, i, 0, 0);
     }
-    SkColorTable* ctable = new SkColorTable(c, 256, kOpaque_SkAlphaType);
+    SkColorTable* ctable = new SkColorTable(c, 256);
 
     SkBitmap bm;
-    bm.allocPixels(SkImageInfo::Make(256, 32, kIndex_8_SkColorType,
-                                     kPremul_SkAlphaType),
+    bm.allocPixels(SkImageInfo::Make(256, 32, kIndex_8_SkColorType, kPremul_SkAlphaType),
                    NULL, ctable);
     ctable->unref();