fix: remove top level is_fabric check

[WoLewicki]

Summary

PR removing top level check for isFabric since it should be evaluated after it is added to global which may not be done at that point.

Test plan

[tomekzaw]

LGTM

[piaskowyk]

Can we be certain that on the very first call to one of those functions, isFabric() will return the correct value?

[WoLewicki]

@piaskowyk I don't think so, I am not fully aware when those checks are used and if they are used before this line:

react-native-reanimated/Common/cpp/ReanimatedRuntime/RNRuntimeDecorator.cpp

Line 30 in 1ab8c22

rnRuntime.global().setProperty(rnRuntime, "_IS_FABRIC", isFabric);

is evaluated then it will not work. I think it is still better than having it in top-level scope.