templates/hooks--*: remove sample hooks without any functionality

Remove the sample post-commit and post-receive hooks.  The sample
post-commit doesn't contain any sample functionality and the comments do
not provide more information than already found in the documentation.
The sample post-receive hooks doesn't provide any sample functionality
either and refers in the comments to a contrib hook that might be
installed in different locations on different systems, which isn't that
helpful.

Signed-off-by: Gerrit Pape <pape@smarden.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>