Revert "manual: Add notes about GitHub and hashes"

This note is no longer needed, so remove it.

Tarballs generated by GitHub are always the same, so hashes can be
checked.

This reverts commit 9474cc2594c8643301164500ce6eb62546da2b8f.

[Thomas: fix other remaining references to not using hashes for
github, as noticed by Maxime Hadjinlian.]

Cc: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

docs/manual/adding-packages-directory.txt

@@ -448,20 +448,12 @@ provide any hash, or only provides an +md5+ hash, then compute at least one
 strong hash yourself (preferably +sha256+, but not +md5+), and mention
 this in a comment line above the hashes.
 
-.Note
-If +libfoo+ is from GitHub (see xref:github-download-url[] for details), we
-can only accept a +.hash+ file if the package is a released (e.g. uploaded
-by the maintainer) tarball. Otherwise, the automatically generated tarball
-may change over time, and thus its hashes may be different each time it is
-downloaded, causing a +.hash+ mismatch for that tarball.
-
 .Note
 The number of spaces does not matter, so one can use spaces (or tabs) to
 properly align the different fields.
 
 The +none+ hash type is reserved to those archives downloaded from a
-repository, like a 'git clone', a 'subversion checkout'... or archives
-downloaded with the xref:github-download-url[github helper].
+repository, like a 'git clone', a 'subversion checkout'...
 
 The example below defines a +sha1+ and a +sha256+ published by upstream for
 the main +libfoo-1.2.3.tar.bz2+ tarball, an +md5+ from upstream and a
@@ -480,7 +472,7 @@ sha256 01ba4719c80b6fe911b091a7c05124b64eeece964e09c058ef8f9805daca546b libfoo-d
 # Locally computed:
 sha256 ff52101fb90bbfc3fe9475e425688c660f46216d7e751c4bbdb1dc85cdccacb9 libfoo-fix-blabla.patch
 
-# No hash for 1234, comes from the github-helper:
+# No hash for 1234:
 none   xxx                                                              libfoo-1234.tar.gz
 ----