Stop building NSS on Windows.

Since the GYP variables use_openssl and build_ssl are both
enabled by default on Windows today, I believe we should be able
to clean up the GYP paths that build NSS for Windows.

BUG=4497
TESTED=Passing tryjobs with --clobber specified.
R=pthatcher@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/50559004

Cr-Commit-Position: refs/heads/master@{#8945}
diff --git a/webrtc/base/base.gyp b/webrtc/base/base.gyp
index fb33f77..0c1ecfa 100644
--- a/webrtc/base/base.gyp
+++ b/webrtc/base/base.gyp
@@ -543,7 +543,7 @@
               'conditions': [
                 # On some platforms, the rest of NSS is bundled. On others,
                 # it's pulled from the system.
-                ['OS == "mac" or OS == "ios" or OS == "win"', {
+                ['OS == "mac" or OS == "ios"', {
                   'dependencies': [
                     '<(DEPTH)/net/third_party/nss/ssl.gyp:libssl',
                     '<(DEPTH)/third_party/nss/nss.gyp:nspr',