Remove the usage of is_win_fastlink GN args

This has been removed from https://crrev.com/c/2071243.

Bug: None
Change-Id: I48a0bccbf84a9ae7a8b6045def544ad1a9f5e83c
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/293080
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Auto-Submit: Daniel.L (Byoungchan) Lee <daniel.l@hpcnt.com>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#39297}

tools_webrtc/mb/mb_config.pyl

@@ -321,7 +321,6 @@
       'openh264',
       'pure_release_bot',
       'x64',
-      'win_fastlink',
     ],
     'win_clang_debug_bot_x64': [
       'clang',
@@ -469,9 +468,6 @@
     'ubsan_vptr': {
       'gn_args': 'is_ubsan_vptr=true is_ubsan_no_recover=true',
     },
-    'win_fastlink': {
-      'gn_args': 'is_win_fastlink=true',
-    },
     'win_undef_unicode': {
       'gn_args': 'rtc_win_undef_unicode=true',
     },