Call prepare in browser

[lhorie]

This fixes a regression in fusion-plugin-rpc-redux-react tests.

As per internal discussion, the prepare call was removed in browser code path because it was assumed to no longer be needed, but this assumption only took into consideration bundle splitting, and not generic usage of prepared. Not calling prepare in browser effectively treats prepared as {defer: true} on the client always.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@648044c). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master     #234   +/-   ##
=========================================
  Coverage          ?   75.09%           
=========================================
  Files             ?       13           
  Lines             ?      261           
  Branches          ?       55           
=========================================
  Hits              ?      196           
  Misses            ?       48           
  Partials          ?       17

Impacted Files	Coverage Δ
src/index.js	71.42% <100%> (ø)

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[old-fusion-bot]

Triggered Fusion.js build verification: https://buildkite.com/uberopensource/fusion-release-verification/builds/1639