Remove angle_libjpeg_turbo_dir fallback after Chromium side fix

This is a follow up of crrev.com/c/2282277. To avoid ANGLE roll failure,
crrev.com/c/2285839 should be landed first.

Bug: None
Change-Id: I41ece21af4b689150d82b0b1bc7eaae21ce23fed
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2286811
Reviewed-by: Jamie Madill <[email protected]>
Commit-Queue: Jiajie Hu <[email protected]>

Author: hujiajie

third_party/BUILD.gn

@@ -10,11 +10,6 @@ import("//third_party/libjpeg.gni")
 
 assert(!is_ios, "This is not used on iOS, don't drag it in unintentionally")
 
-# TODO([email protected]): Define the override in Chromium and remove this.
-if (!defined(angle_libjpeg_turbo_dir)) {
-  angle_libjpeg_turbo_dir = "//third_party/libjpeg_turbo"
-}
-
 config("system_libjpeg_config") {
   libs = [ "jpeg" ]
   defines = [ "USE_SYSTEM_LIBJPEG" ]