Merge #19058: doc: Drop protobuf stuff

ea9fcfd doc: Drop protobuf stuff (Hennadii Stepanov)

Pull request description:

  This is a follow-up to #17165.

ACKs for top commit:
  fanquake:
    ACK ea9fcfd -  clicked the links and they seem to work.

Tree-SHA512: 0861bbac3a3ff781a413e15f5ed02c624bc15d572a001a53cd2fb9f7683456175f69e9d666b72f260abbb5114b67cefca9fada4d179c62384c90479534ae63d5

Author: fanquake

doc/productivity.md

@@ -12,7 +12,7 @@ Table of Contents
    * [Multiple working directories with `git worktrees`](#multiple-working-directories-with-git-worktrees)
    * [Interactive "dummy rebases" for fixups and execs with `git merge-base`](#interactive-dummy-rebases-for-fixups-and-execs-with-git-merge-base)
 * [Writing code](#writing-code)
-   * [Format C/C++/Protobuf diffs with `clang-format-diff.py`](#format-ccprotobuf-diffs-with-clang-format-diffpy)
+   * [Format C/C++ diffs with `clang-format-diff.py`](#format-cc-diffs-with-clang-format-diffpy)
    * [Format Python diffs with `yapf-diff.py`](#format-python-diffs-with-yapf-diffpy)
 * [Rebasing/Merging code](#rebasingmerging-code)
    * [More conflict context with `merge.conflictstyle diff3`](#more-conflict-context-with-mergeconflictstyle-diff3)
@@ -118,13 +118,13 @@ You can also set up [upstream refspecs](#reference-prs-easily-with-refspecs) to
 Writing code
 ------------
 
-### Format C/C++/Protobuf diffs with `clang-format-diff.py`
+### Format C/C++ diffs with `clang-format-diff.py`
 
 See [contrib/devtools/README.md](/contrib/devtools/README.md#clang-format-diff.py).
 
 ### Format Python diffs with `yapf-diff.py`
 
-Usage is exactly the same as [`clang-format-diff.py`](#format-ccprotobuf-diffs-with-clang-format-diffpy). You can get it [here](https://github.com/MarcoFalke/yapf-diff).
+Usage is exactly the same as [`clang-format-diff.py`](#format-cc-diffs-with-clang-format-diffpy). You can get it [here](https://github.com/MarcoFalke/yapf-diff).
 
 Rebasing/Merging code
 -------------