Revert SI-6240 synchronization for runtime reflection

This commit reverts #2083:
  - 387b2590db runtime reflection: death from thousand threads
  - 73d079fb38 removes the assertion in missingHook
  - f4dd56ca5d synchronizes names
  - dd148de5a8 synchronizes pendingVolatiles
  - 4cbb9357c5 synchronizes toolboxes
  - 07bcb6176a SI-7045 reflection now auto-initializes selfType
  - bebd62d566 optimizes Scala reflection GIL
  - 735634f1d6 initializes lazy vals and inner objects in advance
  - 5b37cfb19a introduces GIL to Scala reflection
  - 981da8edfc cleans up initialization of runtime reflection
  - b2c2493b22 reflection no longer uses atPhase and friends
  - a9dca512d8 synchronizes symbols
  - 0262941b3c removes the crazy extraneous log
  - 21d5d3820b moves Symbol#SymbolKind to Symbols

review by @xeno-by or anyone else who can get this done today -- I'd like to end the week with a nice row of happy jenkins jobs (will merge 2.10.x into master after this) /cc @paulp, @gkossakowski 

next week will be the sprint to get M2 out of the door