setup_links.py: Remove third_party/libevent

It no longer exists in this location of Chromium and is thus
no longer needed.

NOTRY=True
TBR=tommi@webrtc.org

Review URL: https://codereview.webrtc.org/1893953002

Cr-Commit-Position: refs/heads/master@{#12398}

.gitignore

@@ -99,7 +99,6 @@
 /third_party/libc++
 /third_party/libc++-static
 /third_party/libc++abi
-/third_party/libevent
 /third_party/libFuzzer
 /third_party/libjingle
 /third_party/libjpeg

setup_links.py

@@ -94,7 +94,6 @@ if 'android' in target_os:
     'third_party/ijar',
     'third_party/jsr-305',
     'third_party/junit',
-    'third_party/libevent',
     'third_party/libxml',
     'third_party/mockito',
     'third_party/modp_b64',