Fix tests - remove folly/File.h import in jsbigstring test (#41059)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/41059

Remove unused import that was breaking tests

Changelog: [Internal]

Reviewed By: NickGerleman

Differential Revision: D50380976

fbshipit-source-id: fab27b52959e74e8ad7a0cdd840e6f496608e380

packages/react-native/ReactCommon/cxxreact/tests/jsbigstring.cpp

@@ -9,7 +9,6 @@
 #include <sys/mman.h>
 
 #include <cxxreact/JSBigString.h>
-#include <folly/File.h>
 #include <gtest/gtest.h>
 
 using namespace facebook::react;