Remove unused flag that should not be used.

We generally shouldn't suppress deprecation warnings but instead fix them.
Temporarily they are sometimes (rarely) ok with a link to a bug for cleaning
up the underlying issue.

In this case, the flag isn't needed, so just remove it.

Bug: none
Change-Id: I0a7be212858118d0f899919024611d3a5d5225a1
Reviewed-on: https://pdfium-review.googlesource.com/c/51110
Auto-Submit: Nico Weber <thakis@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>

skia/BUILD.gn

diff --git a/skia/BUILD.gn b/skia/BUILD.gn
index 1d1ff23..84bdc92 100644
--- a/skia/BUILD.gn
+++ b/skia/BUILD.gn
@@ -378,9 +378,6 @@
       "//third_party/skia/src/utils/mac/SkStream_mac.cpp",
     ]
     set_sources_assignment_filter(sources_assignment_filter)
-
-    # To disable warning "CGContextSelectFont' is deprecated"
-    cflags = [ "-Wno-deprecated-declarations" ]
   }
 
   if (skia_support_pdf) {