Remove a flag to show storage manager in options page.

The flag --enable-storage-manager was used to show/hide storage manager in options page.
The storage manager in options has already been shipped, so we don't need the flag anymore.
Note that the storage manager in MD settings is going to be enabled by a different flag: --enable-md-storage-manager.

BUG=none
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2389793003
Cr-Commit-Position: refs/heads/master@{#424976}
7 files changed