Roll Fuchsia Linux SDK from 4_MXZyYYE... to -kU3jhhRL... (#24850)

https://dart.googlesource.com/external/github.com/flutter/engine/+/4f49758c61d0d219f6a625b3d4fd83c3185b49d1
diff --git a/commits.json b/commits.json
index 1121d10..cd95bf8 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
-  "external/github.com/flutter/engine":"55bb5c909d91af32ef2d2ce439e13a167be4cd73",
+  "external/github.com/flutter/engine":"4f49758c61d0d219f6a625b3d4fd83c3185b49d1",
   "external/github.com/flutter/flutter":"a0ba6464089f906fefbf610732b2c9a7b66a1260",
   "sdk":"8f2ca0b2482bf6acde1e90aab3745de407d4e51a"
 }
\ No newline at end of file