Remove libexif references.

The libexif code were removed in r381121.

Change-Id: Ie66360817896cfbdd2b849c243e7c80d9eeaffd1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2050750Reviewed-by: Tommy Li <tommycli@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742243}

.gn

@@ -435,7 +435,6 @@ check_targets = [
   "//third_party/libc++abi/*",
   "//third_party/libcxx-pretty-printers/*",
   "//third_party/libdrm/*",
-  "//third_party/libexif/*",
   "//third_party/libgav1/*",
   "//third_party/libjingle/*",
 

third_party/.gitignore

@@ -124,7 +124,6 @@
 /libc++-static/libc++.a
 /libaddressinput/src
 /libdrm/src
-/libexif/sources
 /libFuzzer/src
 /libgav1/src
 /libgifcodec