Remove duplicate MSan check

Removes duplicate MSan check in the turbojpeg build target definition.
For MSan builds, the check added a second copy of the jsimd_none.c
file. This causes a linker error, and subsequently a build failure.

Bug: 993876
Change-Id: I6782650d70329eb3628c13b23bd843ef0fa43694
diff --git a/BUILD.gn b/BUILD.gn
index 0be68be..4c45afc 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -296,14 +296,6 @@
   public_deps = [
     ":libjpeg",
   ]
-
-  # MemorySanitizer doesn't support assembly code, so keep it disabled in
-  # MSan builds for now.
-  if (is_msan) {
-    sources += [ "jsimd_none.c" ]
-  } else {
-    public_deps += [ ":simd" ]
-  }
 }
 
 if (build_with_chromium) {