Remove content/ csp from native_types.mojom

content's CSP are gone. They have been merged into network::mojom's CSP.
This patch updates the content/common/native_types.mojom to reflect this.

See UnifyCSP:
https://docs.google.com/document/d/1v5mJnXJ5dSVXE_rgvJnNM9bzH0ni0YzdhPQ7GLqyhao

Bug: 1021462
Change-Id: I1b254e196f5162844d9f9ae2b466b17259d8a07a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2030963
Auto-Submit: Arthur Sonzogni <arthursonzogni@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#737488}

content/common/native_types.mojom

@@ -94,17 +94,5 @@ enum PreferredColorScheme;
 [Native]
 enum SystemThemeColor;
 
-[Native]
-struct ContentSecurityPolicy;
-
-[Native]
-struct CSPDirective;
-
-[Native]
-struct CSPSourceList;
-
-[Native]
-struct CSPSource;
-
 [Native]
 struct CSPViolationParams;