Remove "rescue" clause around "require 'openssl'"

Some `require 'openssl'` statements were surrounded by `rescue` blocks to deal with Ruby versions that did not support `OpenSSL::Digest::SHA1` or `OpenSSL::PKCS5`.

[As @jeremy explains](https://github.com/rails/rails/commit/a6a0904fcb12b876469c48b1c885aadafe9188cf#commitcomment-8826666) in the original commit:

> If jruby didn't have jruby-openssl gem, the require wouldn't work. Not sure whether either of these are still relevant today.

According to the [release notes for JRuby 1.7.13](http://www.jruby.org/2014/06/24/jruby-1-7-13.html):

> jruby-openssl 0.9.5 bundled

which means the above `rescue` block is not needed anymore.

All the Ruby versions supported by the current version of Rails provide those OpenSSL libraries, so Travis CI should also be happy by removing the `rescue` blocks.

---

Just to confirm, with JRuby:

    $ ruby --version #=> jruby 1.7.16.1 (1.9.3p392) 2014-10-28 4e93f31 on Java HotSpot(TM) 64-Bit Server VM 1.8.0_20-b26 +jit [darwin-x86_64]
    $ irb
    irb(main):001:0> require 'openssl' #=> true
    irb(main):002:0> OpenSSL::Digest::SHA1 #=> OpenSSL::Digest::SHA1
    irb(main):003:0> OpenSSL::PKCS5 # => OpenSSL::PKCS5

And with Ruby 2.1:

    $ ruby --version #=> ruby 2.1.2p95 (2014-05-08 revision 45877) [x86_64-darwin13.0]
    $ irb
    irb(main):001:0> require 'openssl' #=> true
    irb(main):002:0> OpenSSL::Digest::SHA1 #=> OpenSSL::Digest::SHA1
    irb(main):003:0> OpenSSL::PKCS5 #=> OpenSSL::PKCS5
Merge pull request #17903 from claudiob/remove-rescue-openssl

Remove "rescue" clause around "require 'openssl'"