Remove unused SILENT macro; remove duplicate MacOS_Test_config.h file

Remove unused SILENT macro; remove duplicate MacOS_Test_config.h file

* Mac_files/MacOS_Test_config.h: Remove.
* Mac_files/MacOS_config.h: Expand tabs to spaces.
* Mac_files/MacOS_config.h (SILENT): Remove unused macro.
* windows-untested/stdafx.h (SILENT): Likewise.
* Mac_files/MacOS_config.h: Remove GC tuning macros description.
* Makefile.am (EXTRA_DIST): Remove MacOS_Test_config.h entry.
* Makefile.direct (OTHER_FILES): Likewise.
* Makefile.dj (OTHER_FILES): Likewise.
* doc/README.Mac: Update (remove info about MacOS_Test_config.h and
SILENT macro).