[analyzer] Remove getEngine() form CheckerContext

A step toward making sure that diagnostics report should only
be generated though the CheckerContext and not though BugReporter
or ExprEngine directly.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@142947 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed