Revert "Mark pdfium chromium_code."

This reverts most of https://codereview.chromium.org/1557923004/

Doesn't build on the chromeos bots yet.

BUG=pdfium:29
TBR=thestig

Review URL: https://codereview.chromium.org/1561013002 .
diff --git a/pdfium.gyp b/pdfium.gyp
index 9c47018..4e93279 100644
--- a/pdfium.gyp
+++ b/pdfium.gyp
@@ -4,7 +4,8 @@
 
 {
   'variables': {
-    'chromium_code': 1,
+    # TODO(thakis): Enable this, pdfium:29
+    #'chromium_code': 1,
     'pdf_use_skia%': 0,
     'pdf_enable_v8%': 1,
     'conditions': [