git-branch: change "upstream" --> "remote"

"upstream" is often used as a synonym for "remote", but we probably should avoid promoting that equivalence, since the terms "upstream" and "downstream" have specific meanings in the context of software dependency, which don't necessarily map with the meanings of "local" and "remote" in the context of computer networks in general (and distributed networks of git repositories in particular).

pages/common/git-push.md

@@ -1,6 +1,6 @@
 # git push
 
-> Push commits to a remote (upstream) repository.
+> Push commits to a remote repository.
 
 - Send local changes in the current branch to its remote counterpart:
 
@@ -10,7 +10,7 @@
 
 `git push {{remote_name}} {{local_branch}}`
 
-- Publish the current branch to a remote repository, setting the upstream branch name:
+- Publish the current branch to a remote repository, setting the remote branch name:
 
 `git push {{remote_name}} -u {{remote_branch}}`