readme: remove LGTM and Travis and add CodeQL badge

since both CI systems have been removed we no longer require the badges/links.
LGTM has been replaced by CodeQL which we now have as badge.

README.md

@@ -2,8 +2,7 @@ srsRAN
 ======
 
 [![Build Status](https://github.com/srsran/srsRAN/actions/workflows/ccpp.yml/badge.svg?branch=master)](https://github.com/srsran/srsRAN/actions)
-[![Build Status](https://app.travis-ci.com/srsran/srsRAN.svg?branch=master)](https://app.travis-ci.com/github/srsran/srsRAN)
-[![Language grade: C/C++](https://img.shields.io/lgtm/grade/cpp/g/srsran/srsRAN.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/srsran/srsRAN/context:cpp)
+[![CodeQL](https://github.com/srsran/srsRAN/actions/workflows/codeql.yml/badge.svg?branch=master)](https://github.com/srsran/srsRAN/actions/workflows/codeql.yml)
 [![Coverity](https://scan.coverity.com/projects/23045/badge.svg)](https://scan.coverity.com/projects/srsran)
 
 srsRAN is a 4G/5G software radio suite developed by [SRS](http://www.srs.io).