scripts: remove github-merge.py

This script has been moved to the bitcoin-core/bitcoin-maintainer-tools repository,
after discussion in a core dev meeting. The rationale being that it is also useful to
other projects, and thus should be moved to a more general repository.

Meeting log: http://www.erisian.com.au/bitcoin-core-dev/log-2019-08-15.html
See also: bitcoin-core/bitcoin-maintainer-tools#28

contrib/README.md

@@ -3,10 +3,9 @@ Repository Tools
 
 ### [Developer tools](/contrib/devtools) ###
 Specific tools for developers working on this repository.
-Contains the script `github-merge.py` for merging GitHub pull requests securely and signing them using GPG.
 
 ### [Verify-Commits](/contrib/verify-commits) ###
-Tool to verify that every merge commit was signed by a developer using the above `github-merge.py` script.
+Tool to verify that every merge commit was signed by a developer using the `github-merge.py` script.
 
 ### [Linearize](/contrib/linearize) ###
 Construct a linear, no-fork, best version of the blockchain.

contrib/devtools/README.md

@@ -89,32 +89,6 @@ example:
 BUILDDIR=$PWD/build contrib/devtools/gen-manpages.sh
 ```
 
-github-merge.py
-===============
-
-A small script to automate merging pull-requests securely and sign them with GPG.
-
-For example:
-
-  ./github-merge.py 3077
-
-(in any git repository) will help you merge pull request #3077 for the
-bitcoin/bitcoin repository.
-
-What it does:
-* Fetch master and the pull request.
-* Locally construct a merge commit.
-* Show the diff that merge results in.
-* Ask you to verify the resulting source tree (so you can do a make
-check or whatever).
-* Ask you whether to GPG sign the merge commit.
-* Ask you whether to push the result upstream.
-
-This means that there are no potential race conditions (where a
-pullreq gets updated while you're reviewing it, but before you click
-merge), and when using GPG signatures, that even a compromised GitHub
-couldn't mess with the sources.
-
 Setup
 ---------
 Configuring the github-merge tool for the bitcoin repository is done in the following way: