cpp-common: add vectorFastRemove

cpp-common: add vectorFastRemove

Add the vectorFastRemove function, in src/cpp-common/vector.hpp, as a
drop-in replacement for g_ptr_array_remove_index_fast, when replacing a
GPtrArray with an std::vector.

Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Change-Id: Ibee249fd9a8168d02ad99abf36984bf7edd53b5b
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/8493
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>