This CL a logical revert of a previous CL [1], which separated Java
files into common ones and overridable ones.  Now that that overriding
concept is no longer used, there is no need to keep having separate
directory structure.

 [1]: Ic734bd4d20aa050c688a3158b1a382ae0ac18991
      fb74ab15

Fix: 79323502
Test: make -j aosp_taimen-userdebug && make -j
Test: tapas LatinIME && make -j
Change-Id: I2090bc25d18e6d4f24e91c2cbfe832755cbb4e8f

Bug 20701628.

Change-Id: Ifba1e7dd7f9934c8c13279dfb95bf02c0e30e650

This CL also adds @SuppressWarning("unused" to java-overridable package.

Bug: 18003991
Change-Id: If70527e30654384705d7a814f5efd181d9f539e1

This should make IDEs happy with appropriate source code directory
selection.

Change-Id: Ic734bd4d20aa050c688a3158b1a382ae0ac18991
(cherry picked from commit fb74ab15)

This should make IDEs happy with appropriate source code directory
selection.

bug: 16829244
Change-Id: Ic734bd4d20aa050c688a3158b1a382ae0ac18991

Bug: 8651863
Change-Id: I748f35726d72ede926d5b06ed87ff029317f1ac3

Bug: 7600384
Change-Id: Ic5dbbbbcf19d778dde1316ebb417f1a8ede2d25d

Bug: 8161354
Change-Id: I17c23f56dd3bc2f27726556bf2c5a9d5520bd172