Switch to Ruby 1.9.3. Replace .rvmrc with .ruby-(version|gemset) files.

# Overview
Update Ruby version and replace `.rvmrc` with standardized files.

# Changes
* Switch to Ruby 1.9.3 in `.ruby-version`.
* Replace `.rvmrc` with `.ruby-version` and `.ruby-gemset`.

# Tasks
* Task 11017

# Tests
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15 examples, 0 failures
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