Rename CPDFDoc_Environment to CPDFSDK_Environment

CPDFDoc_Environment does not fit with the general naming scheme of the rest of
the files in fpdfsdk. This CL updates the naming to CPDFSDK_Environment to
better fit with the surrounding files.

Review-Url: https://codereview.chromium.org/2333413003
diff --git a/fpdfsdk/formfiller/cffl_combobox.h b/fpdfsdk/formfiller/cffl_combobox.h
index 6b8fb49..b9e7430 100644
--- a/fpdfsdk/formfiller/cffl_combobox.h
+++ b/fpdfsdk/formfiller/cffl_combobox.h
@@ -21,7 +21,7 @@
 
 class CFFL_ComboBox : public CFFL_FormFiller, public IPWL_FocusHandler {
  public:
-  CFFL_ComboBox(CPDFDoc_Environment* pApp, CPDFSDK_Annot* pWidget);
+  CFFL_ComboBox(CPDFSDK_Environment* pApp, CPDFSDK_Annot* pWidget);
   ~CFFL_ComboBox() override;
 
   // CFFL_FormFiller: