CMake install: fix Hydra plugin path and include all built delegates

plugin/usd without a trailing slash made CMake install the directory
itself under bin/usd/, landing plugins at bin/usd/usd/hdStorm/ etc.
(one level too deep). Adding the trailing slash installs the contents
directly into bin/usd/, matching the build-directory layout that
POST_BUILD produces via copy_directory.

Also removed the now-redundant install(FILES hdStorm.dll DESTINATION bin)
which was placing the DLL in the exe root instead of bin/usd/ where
plugInfo.json's LibraryPath expects it.

hdEmbree, hdArnold, and hdCycles install rules were already correct
(they explicitly target bin/usd/); this change makes the base USD
plugin/usd contents consistent with them.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CMakeLists.txt

@@ -365,14 +365,10 @@ install(DIRECTORY ${OpenUSD_ROOT_DIR}/lib/usd
     DESTINATION bin
 )
 
-install(DIRECTORY ${OpenUSD_ROOT_DIR}/plugin/usd
+install(DIRECTORY ${OpenUSD_ROOT_DIR}/plugin/usd/
     DESTINATION bin/usd
 )
 
-install(FILES ${OpenUSD_ROOT_DIR}/plugin/usd/hdStorm.dll
-    DESTINATION bin
-)
-
 if(OPENUSD_HAS_EMBREE)
     # Install to bin/usd/ so plugInfo.json's LibraryPath "../hdEmbree.dll" resolves correctly.
     install(FILES "${HDEMBREE_DLL}"