Remove -swift-version 3 checks for "expression too complex".

[rudkx]

This was initially added to avoid "expression was too complex" in a
case where we were not previously reporting it for -swift-version 3
but should have been. In retrospect this seems misguided since
although we would not like to regress on "too complex" expressions, we
really don't want to silently continue in the cases where we decide an
expression is "too complex", but where we have a solution that we
could use. It's better to fail.

[rudkx]

@swift-ci Please smoke test and merge

[rudkx]

@swift-ci Please smoke test and merge

[rudkx]

@swift-ci Please smoke test

[rudkx]

Hmmm, Linux failed with:

note: testing using 'lldb': /home/buildnode/jenkins/workspace/swift-PR-Linux-smoke-test@3/branch-master/buildbot_linux/none-swift_package_sandbox_linux-x86_64/usr/bin/lldb
lit.py: /home/buildnode/jenkins/workspace/swift-PR-Linux-smoke-test@3/branch-master/swift-integration-tests/lit.cfg:180: fatal: lldb does not exist!
/home/buildnode/jenkins/workspace/swift-PR-Linux-smoke-test@3/branch-master/swift/utils/build-script: fatal error: command terminated with a non-zero exit status 2, aborting
/home/buildnode/jenkins/workspace/swift-PR-Linux-smoke-test@3/branch-master/swift/utils/build-script: fatal error: command terminated with a non-zero exit status 1, aborting
Build step 'Execute shell' marked build as failure

[rudkx]

@swift-ci Please smoke test Linux platform

[rudkx]

@swift-ci Please clean smoke test Linux platform

[gottesmm]

@rudkx I think lldb has broken PR testing now.