Bug #169: Removed unnecessary null pointer checks

Explicit null pointer checks were performed at some source code places
before pointers were passed to the C++ delete operator. This was unnecessary
because the delete operator will care for such parameter validation already.
http://www.parashift.com/c++-faq/delete-handles-null.html

Redundant checks were removed.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: John Peterson <jwpeterson@gmail.com>
Merge branch 'Remove_unnecessary_null_pointer_checks'