Remove special member defaulting as compiler does it implicitely.
Remove special member defaulting as compiler does it implicitely.

Providing our two constructors does not prevent the compiler from
implicitely generating the other special members implicitely.

Reference:

- http://accu.org/content/conf2014/Howard_Hinnant_Accu_2014.pdf

daniel-j-h/toy-osm-spatial-index