build: recommend fewer VS Code extensions

Some of the recommendations are not that useful and might rather annoy
contributors:

* ms-azuretools.vscode-docker, not needed nor useful in dev container
* tamasfe.even-better-toml, right now there is only one toml file
* tdennis4496.cmantic, unmaintained and questionaable usefulness
* twxs.cmake, incorporated in ms-vscode.cmake-tools
* xaver.clang-format, not needed to apply clang-format
* eamodio.gitlens, very subjective usefulness
* cheshirekow.cmake-format, unmaintained
* GitHub.vscode-pull-request-github, very subjective usefulness

.vscode/extensions.json

@@ -2,20 +2,14 @@
   "recommendations": [
     "esbenp.prettier-vscode",
     "llvm-vs-code-extensions.vscode-clangd",
-    "ms-azuretools.vscode-docker",
     "ms-vscode.cmake-tools",
     "ms-vscode.cpptools",
     "ms-vscode.cpptools-extension-pack",
     "ms-vscode.cpptools-themes",
     "tamasfe.even-better-toml",
-    "tdennis4496.cmantic",
     "twxs.cmake",
-    "xaver.clang-format",
     "vadimcn.vscode-lldb",
     "42crunch.vscode-openapi",
-    "eamodio.gitlens",
     "redhat.vscode-yaml",
-    "cheshirekow.cmake-format",
-    "GitHub.vscode-pull-request-github"
   ]
 }