context: stop catching TypeError when converting hex nodeid to binary
It has been a programming error to pass a 40-character string that is
not a hex nodeid since 8b86acc7aa64 (context: drop support for looking
up context by ambiguous changeid (API), 2018-04-28), so we can just
let it raise a TypeError.
Differential Revision: https://phab.mercurial-scm.org/D4807
(binary:application/octet-stream)