ci: disable deprecated warnings for windows GHA builds (#14875)

Author: scotthart

cmake/GoogleCloudCppCommonOptions.cmake

@@ -80,6 +80,7 @@ function (google_cloud_cpp_add_common_options target)
             return()
         endif ()
         target_compile_options(${target} PRIVATE "/W3")
+        target_compile_options(${target} PRIVATE "/wd4996")
         if (GOOGLE_CLOUD_CPP_ENABLE_WERROR)
             target_compile_options(${target} PRIVATE "/WX")
         endif ()

google/cloud/bigtable/test_proxy/BUILD.bazel

@@ -22,7 +22,6 @@ cc_library(
     testonly = True,
     srcs = ["cbt_test_proxy.cc"],
     hdrs = ["cbt_test_proxy.h"],
-    copts = ["-Wno-deprecated-declarations"],
     deps = [
         "//:bigtable",
         "//protos:system_includes",