switched SkSL's temporary 'highfloat' type back to 'float'

Bug: skia:
Change-Id: If0debae7318b6b5b4a7cb85d458996a09931127e
Reviewed-on: https://skia-review.googlesource.com/48760
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/vk/GrVkCopyManager.cpp b/src/gpu/vk/GrVkCopyManager.cpp
index 7ab47e9..d27997d 100644
--- a/src/gpu/vk/GrVkCopyManager.cpp
+++ b/src/gpu/vk/GrVkCopyManager.cpp
@@ -47,7 +47,7 @@
             "half4 uPosXform;"
             "half4 uTexCoordXform;"
         "};"
-        "layout(location = 0) in highfloat2 inPosition;"
+        "layout(location = 0) in float2 inPosition;"
         "layout(location = 1) out half2 vTexCoord;"
 
         "// Copy Program VS\n"