Vulkan: Simplify shader interface variable map The shader interface variable map had a "resource index" -> info map to optimize descriptor set building. That avoided hashing the resource name when the rest of the map was name-based. With the map using SPIR-V ids now, there is no reason to maintain this map; SPIR-V ids can be used to look up the info just as efficiently. Bug: angleproject:7220 Change-Id: I619783dce558a59184955cc314c1f41e6733f1b7 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4630728 Reviewed-by: Charlie Lao <cclao@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Yuxin Hu <yuxinhu@google.com>