SI-7603 Remove diagnostic code for annotation error

We've fingered the true culprit in the previous commit.
kills introduceTopLevel

As we've figured out from the practice, introduceTopLevel is seductively
useful but unfortunately not robust, potentially bringing compilation
order problems.

Therefore, as discussed, I'm removing it from the public macro API.
Alternatives are either: 1) delving into internals, or
2) using macro paradise and experimenting with macro annotations:
http://docs.scala-lang.org/overviews/macros/annotations.html.
Merge pull request #2798 from som-snytt/issue/7544-errmsg

SI-7544 Interpolation message for %% literal
Merge pull request #2785 from soc/SI-7704

SI-7704 Fix partest's test category selection
Merge pull request #2803 from adriaanm/rebase-2728

SI-7658 Prevent StackOverflowError in ScalaRunTime.stringOf
Merge pull request #2821 from xeno-by/topic/fundep-materialization

SI-7470 implements fundep materialization
Merge pull request #2823 from som-snytt/issue/7715

SI-7715 String inpatternation s"$_" for s"${_}"
Merge pull request #2830 from densh/topic/stats-parsing-2

updated SI-7331, SI-6843, SI-7731, parser entry point refactoring, assertThrows utility function
Merge pull request #2777 from soc/SI-7681-dead-code-daemonthreadfactory

SI-7681 Remove DaemonThreadFactory, clean up IMain
Merge pull request #2836 from soc/SI-7564-redux

SI-7564 [Avian] Whitespace fixes to run/tailcalls.check
Merge pull request #2842 from retronym/ticket/7603-2

SI-7603 Fix thread safety of FlagTranslation
Merge pull request #2838 from retronym/ticket/7716

SI-7716 Exclude patmat synthetics from bounds checking
Merge pull request #2837 from soc/SI-7630

SI-7630 [Avian] Skip test run/repl-javap-outdir-funs on Avian
Merge pull request #2841 from gourlaysama/wip/t6507

SI-6507 do not call .toString on REPL results when :silent is on.
Merge pull request #2843 from xeno-by/topic/kill-introduce-top-level

kills introduceTopLevel
SI-7704 Fix partest's test category selection (again)

Looks like multiple, different fixes for this issue managed to break it
again.
Merge pull request #2845 from soc/SI-7704-redux

SI-7704 Fix partest's test category selection (again)
Crasher in symbol tracer.
Repair NPE in -Ytyper-debug output.
Make memberType less crashy.

It's a source of constant peril that sym.tpe on NoSymbol
is fine (it's NoType) but tpe memberType sym on NoSymbol throws
a NSDNHO. The last thing we should be doing is discouraging
people from using memberType in favor of sym.tpe, the latter
being almost always the wrong thing.