doc: Remove .gitignore section

This was added to the gitignore file itself in commit
fada115cbe. The past violations are
evidence that the note in the dev notes was missed anyway.

doc/developer-notes.md

@@ -785,38 +785,6 @@ Threads
   - [ThreadI2PAcceptIncoming (`b-i2paccept`)](https://doxygen.bitcoincore.org/class_c_connman.html#a57787b4f9ac847d24065fbb0dd6e70f8)
     : Listens for and accepts incoming I2P connections through the I2P SAM proxy.
 
-Ignoring IDE/editor files
---------------------------
-
-In closed-source environments in which everyone uses the same IDE, it is common
-to add temporary files it produces to the project-wide `.gitignore` file.
-
-However, in open source software such as Bitcoin Core, where everyone uses
-their own editors/IDE/tools, it is less common. Only you know what files your
-editor produces and this may change from version to version. The canonical way
-to do this is thus to create your local gitignore. Add this to `~/.gitconfig`:
-
-```
-[core]
-        excludesfile = /home/.../.gitignore_global
-```
-
-(alternatively, type the command `git config --global core.excludesfile ~/.gitignore_global`
-on a terminal)
-
-Then put your favourite tool's temporary filenames in that file, e.g.
-```
-# NetBeans
-nbproject/
-```
-
-Another option is to create a per-repository excludes file `.git/info/exclude`.
-These are not committed but apply only to one repository.
-
-If a set of tools is used by the build system or scripts the repository (for
-example, lcov) it is perfectly acceptable to add its files to `.gitignore`
-and commit them.
-
 Development guidelines
 ============================