Remove unused variables.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
rm ancient error for lowercase kinds

3 of these kinds no longer even exist in the CamelCase form
remove `copy` as a keyword
make `in` and `foreach` get treated as keywords
convert `pure` to a reserved keyword
auto merge of #8162 : thestinger/rust/no-copy, r=brson
auto merge of #8149 : omasanori/rust/cleanup, r=alexcrichton

Fixed a warning.