Remove methods in Block deprecated in 1.18

Remove methods in Block deprecated in 1.18

One use found in core or Gerrit extensions which was replaced.

* Block::clear() (deprecated in 1.18)
* Block::decodeExpiry() (deprecated in 1.18)
* Block::encodeExpiry() (deprecated in 1.18)
* Block::forUpdate() (deprecated in 1.18)
* Block::infinity() (deprecated in 1.18)
* Block::load() (deprecated in 1.18)
* Block::newFromDB() (deprecated in 1.18)
* Block::normaliseRange() (deprecated in 1.18)
* Block::parseExpiryInput() (deprecated in 1.18)

Change-Id: Ia8ea6b5248111326f929062346f3868a0550421b