win: Remove a few /wd flags

/wd have (almost) no effect on clang-cl, and we no longer use cl.exe

Bug: 1053958
Change-Id: I96f9cb49306e3ac4549beb6d670a03d9d2f52ecd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3252498
Reviewed-by: Hans Wennborg <hans@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Reviewed-by: Sunny Sachanandani <sunnyps@chromium.org>
Cr-Commit-Position: refs/heads/main@{#937832}
NOKEYCHECK=True
GitOrigin-RevId: ff5d49d3942e27f495e6a1a7a40a85f3a1d23814
diff --git a/BUILD.gn b/BUILD.gn
index bce8fe4..6645b52 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -146,14 +146,6 @@
       cflags_cc += [ "-Wbitfield-enum-conversion" ]
     }
   }
-  if (is_win) {
-    cflags_cc += [
-      "/wd4005",  # macro-redefinition
-      "/wd4018",  # sign-compare
-      "/wd4068",  # unknown pragma
-      "/wd4702",  # unreachable code
-    ]
-  }
 }
 
 config("absl_test_cflags_cc") {