Remove ptmalloc from source tree

Remove ptmalloc from source tree

This malloc-replacement library is marked experimental and disabled by
default. It is also Unix-only.

On linux (GNU C library, actually) ptmalloc graduated to become the
native allocator, according to its webpage (http://www.malloc.de/en/),
making the need to have a copy here significantly lower.

Anyway, there is nothing preventing interested parties from adding this
library to their own setup and very little value in keeping it around in
qtbase.

Change-Id: I2b1c798ca38b59bb767b44d6e5190080ec6ecdf4
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>