Clean up the initialization of instance variables in ScrollView
Clean up the initialization of instance variables in ScrollView

Summary:
This is a small cleanup to move initialization out of the `constructor` as it is unnecessary, and it is currently double initializing a few values.

Changelog:
[General][Changed] Clean up the initialization of instance variables in ScrollView

Reviewed By: nadiia

Differential Revision: D27631320

fbshipit-source-id: 762277e4993a9ce86d444ff2d9e845c93e94d1a8

myntra/react-native,myntra/react-native,myntra/react-native,facebook/react-native,facebook/react-native,javache/react-native,pandiaraj44/react-native,arthuralee/react-native,janicduplessis/react-native,facebook/react-native,javache/react-native,javache/react-native,janicduplessis/react-native,javache/react-native,pandiaraj44/react-native,pandiaraj44/react-native,facebook/react-native,facebook/react-native,javache/react-native,arthuralee/react-native,javache/react-native,janicduplessis/react-native,pandiaraj44/react-native,pandiaraj44/react-native,arthuralee/react-native,javache/react-native,myntra/react-native,pandiaraj44/react-native,myntra/react-native,facebook/react-native,pandiaraj44/react-native,arthuralee/react-native,javache/react-native,janicduplessis/react-native,javache/react-native,arthuralee/react-native,facebook/react-native,pandiaraj44/react-native,myntra/react-native,janicduplessis/react-native,janicduplessis/react-native,myntra/react-native,janicduplessis/react-native,myntra/react-native,myntra/react-native,janicduplessis/react-native,facebook/react-native,facebook/react-native