Autogen: Revert changes to generate moc/rcc in subdirectories

Revert these commits:

* v3.6.0-rc1~134^2
  Tests: QtAutogen: Same source name in different directories test, 2016-04-13
* v3.6.0-rc1~134^2~1
  Autogen: Generate qrc_NAME.cpp files in subdirectories, 2016-04-19
* v3.6.0-rc1~134^2~2
  Autogen: Generate not included moc files in subdirectories, 2016-04-19

They regress existing builds that depend on the paths/symbols generated
previously.  Another approach will be needed to solve the name collision
problem they were intended to solve.  Leave the error diagnostics for
the colliding cases that were added in the same topic as the above
commits because they provide a useful early failure in relevant cases.

Fixes #16209.