Delete iOS9 BUCK workarounds

Summary:
Changelog: [Internal]

According to D19411886 (30491a2085), there were some deps that required a couple targets to stay at iOS9:

- `//fbobjc/Libraries/FBGraphQLQuery:FBGraphQLQuery --> //xplat/js/react-native-github:RCTCxxUtilsApple`
- `//fbobjc/Libraries/NativeTemplateKit:NativeTemplateKitJSExecutorPlugin --> //xplat/js/react-native-github/ReactCommon/jsi:JSCRuntimeApple`

These targets seem to build after this diff, so I guess they've been pushed past iOS9.

Reviewed By: fkgozali

Differential Revision: D25692640

fbshipit-source-id: 1ce94a452090032ef316a3daa79885a7c58d6eac

ReactCommon/jsi/BUCK

@@ -79,8 +79,6 @@ rn_xplat_cxx_library(
     fbobjc_frameworks = [
         "$SDKROOT/System/Library/Frameworks/JavaScriptCore.framework",
     ],
-    # TODO (T55502220): Remove when iOS 9.0 deprecation is complete everywhere.
-    fbobjc_target_sdk_version = "9.0",
     labels = ["supermodule:xplat/default/public.react_native.infra"],
     platforms = APPLE,
     visibility = ["PUBLIC"],