[analyzer] Don't show "Entered 'foo'" if 'foo' is implicit.

Before:
  Calling implicit default constructor for 'Foo'  (where Foo is constructed)
  Entered call from 'test'  (at "=default" or 'Foo' declaration)
  Calling default constructor for 'Bar'  (at "=default" or 'Foo' declaration)

After:
  Calling implicit default constructor for 'Foo'  (where Foo is constructed)
  Calling default constructor for 'Bar'  (at "=default" or 'Foo' declaration)

This only affects the plist diagnostics; this note is never shown in the
other diagnostics.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172915 91177308-0d34-0410-b5e6-96231b3b80d8