Remove references to platformsdk_win(7|8)

These third_party directories were recently removed from DEPS. This
removes a couple of references to them.

R=scottmg@chromium.org
BUG=149684

Review-Url: https://codereview.chromium.org/2611053002
Cr-Commit-Position: refs/heads/master@{#441719}

.gitignore

@@ -419,8 +419,6 @@ vs-chromium-project.txt
 /third_party/pdfium
 /third_party/pefile
 /third_party/perl
-/third_party/platformsdk_win7
-/third_party/platformsdk_win8
 /third_party/ppapi
 /third_party/psyco_win32
 /third_party/pthreads-win32

tools/licenses.py

@@ -78,8 +78,6 @@
 
     # Redistribution does not require attribution in documentation.
     os.path.join('third_party','directxsdk'),
-    os.path.join('third_party','platformsdk_win2008_6_1'),
-    os.path.join('third_party','platformsdk_win7'),
 
     # For testing only, presents on some bots.
     os.path.join('isolate_deps_dir'),