Remove LGTM support (GH #3068)

Since LGTM is sunsetting in a couple of weeks replaced by a
GitHub Action

doc/dev_ref/continuous_integration.rst

@@ -25,15 +25,6 @@ cache locations.
 Then ``src/scripts/ci_build.py`` is invoked to steer the actual build and test
 runs.
 
-LGTM
----------
-
-https://lgtm.com/projects/g/randombit/botan/
-
-An automated linter that is integrated with Github. It automatically checks each
-incoming PR. It also supports custom queries/alerts, which likely would be worth
-investigating but is not something currently in use.
-
 Coverity
 ---------
 

readme.rst

@@ -44,10 +44,6 @@ such as Fedora, Debian, Arch and Homebrew.
     :target: https://codecov.io/github/randombit/botan
     :alt: Code coverage report
 
-.. image:: https://img.shields.io/lgtm/alerts/g/randombit/botan.svg
-    :target: https://lgtm.com/projects/g/randombit/botan/alerts/
-    :alt: LGTM alerts
-
 .. image:: https://oss-fuzz-build-logs.storage.googleapis.com/badges/botan.svg
     :target: https://oss-fuzz.com/coverage-report/job/libfuzzer_asan_botan/latest
     :alt: OSS-Fuzz status

src/lib/tls/tls_signature_scheme.cpp

@@ -321,9 +321,9 @@ bool Signature_Scheme::is_suitable_for(const Private_Key &private_key) const noe
    if(keylen <= 250)
       return false;
 
-   if(m_code == ECDSA_SHA256 && !(keylen >= 250 && keylen <= 350)) // lgtm [cpp/constant-comparison]
-      return false;                                                // `keylen >= 250` will always be true, because keylen <= 250
-                                                                   // was checked before. Leaving it in for readability.
+   if(m_code == ECDSA_SHA256 && !(keylen >= 250 && keylen <= 350))
+      return false;
+
    if(m_code == ECDSA_SHA384 && !(keylen >= 350 && keylen <= 450))
       return false;