Replace SkPin32 with SkTPin and remove.

SkPin32 is already just forwarding to SkTPin, so convert existing
users and remove SkPin32.

Review URL: https://codereview.chromium.org/1314583003
diff --git a/src/core/SkString.cpp b/src/core/SkString.cpp
index 9110d80..d93f662 100644
--- a/src/core/SkString.cpp
+++ b/src/core/SkString.cpp
@@ -509,7 +509,7 @@
 }
 
 void SkString::insertHex(size_t offset, uint32_t hex, int minDigits) {
-    minDigits = SkPin32(minDigits, 0, 8);
+    minDigits = SkTPin(minDigits, 0, 8);
 
     static const char gHex[] = "0123456789ABCDEF";