Remove remaining references to deprecated LGTM (fix for #3958)

Signed-off-by: Stefan Weil <sw@weilnetz.de>

.lgtm.yml

@@ -1,18 +0,0 @@
-extraction:
-  cpp:
-    prepare:
-      packages:
-        - libpango1.0-dev
-    configure:
-      command:
-        - ./autogen.sh
-        - mkdir _lgtm_build_dir
-        - cd _lgtm_build_dir
-        - ../configure
-    index:
-      build_command:
-        - cd _lgtm_build_dir
-        - make training
-  python:
-    python_setup:
-      version: 3

CONTRIBUTING.md

@@ -77,4 +77,4 @@ In short, after running `configure` from the build directory of your choice, to
 
 As soon as your changes are building and tests are succeeding, you can publish them. If you have not already, please [fork](https://docs.github.com/en/get-started/quickstart/contributing-to-projects) tesseract (somewhere) on GitHub, and push your changes to that fork (in a new branch). Then [submit as PR](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request-from-a-fork).
 
-Please also keep track of reports from CI (automated build status) and Coverity/LGTM (quality scan). When the indicators show deterioration after your changes, further action may be required to improve them.
+Please also keep track of reports from CI (automated build status) and Coverity/CodeQL (quality scan). When the indicators show deterioration after your changes, further action may be required to improve them.