Replace `unimpl` comments with `= delete`.

A handful of `unimpl`ed copy constructors were actually supplied as
{} instead of being left unimplemented, but they were not actually used.

Change-Id: I9b88173aeb0cc87f793ee40dfba1b5e5a06d7497
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/308565
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/src/gpu/GrTextureProxyCacheAccess.h b/src/gpu/GrTextureProxyCacheAccess.h
index 26478c6..2590131 100644
--- a/src/gpu/GrTextureProxyCacheAccess.h
+++ b/src/gpu/GrTextureProxyCacheAccess.h
@@ -24,8 +24,8 @@
     }
 
     explicit CacheAccess(GrTextureProxy* textureProxy) : fTextureProxy(textureProxy) {}
-    CacheAccess(const CacheAccess&) {} // unimpl
-    CacheAccess& operator=(const CacheAccess&); // unimpl
+    CacheAccess(const CacheAccess&) = delete;
+    CacheAccess& operator=(const CacheAccess&) = delete;
 
     // No taking addresses of this type.
     const CacheAccess* operator&() const;