Drop the CXX_RVALUE_REFERENCES compiler feature

Whereas the move semantics is accessible on all the supported platorms
(even though it is allowed to be used only in exceptional cases)
there is no need to have a compiler feature for that.

Removal of the CXX_RVALUE_REFERENCES compiler feature gives
a certain code simplification, especially within OwnPtr class.

Also drop move constructors for KURL and Length. 
(Please let me know if you see a performance impact
from this.) Keep move constructors for OwnPtr, RefPtr,
Vector under the 'allowed in exceptional cases' rule
on chromium-cpp.appspot.com.

Review URL: https://codereview.chromium.org/671433003

git-svn-id: svn://svn.chromium.org/blink/trunk@184930 bbb929c8-8fbe-4397-9dbb-9b2b20218538