CI: travis-ci: drop coverity scan builds

we ran out of travis-ci minutes on December 2020. I would keep
exotic architectures like arm64, s390, ppc64le on travis and move
Coverity scan to Github Actions.

so, let us drop coverity scan from travis-ci.

.travis.yml

@@ -46,17 +46,6 @@ matrix:
     compiler: gcc
     env: TARGET=linux-glibc
     name: openssl-1.1.1
-  - os: linux
-    if: type == cron
-    compiler: clang
-    env: TARGET=linux-glibc COVERITY_SCAN_PROJECT_NAME="Haproxy" COVERITY_SCAN_BRANCH_PATTERN="*" COVERITY_SCAN_NOTIFICATION_EMAIL="chipitsine@gmail.com" COVERITY_SCAN_BUILD_COMMAND="make CC=clang DEFINE=-DDEBUG_USE_ABORT TARGET=$TARGET $FLAGS 51DEGREES_SRC=$FIFTYONEDEGREES_SRC DEBUG_STRICT=1"
-    script:
-      - |
-        if [ ! -z ${COVERITY_SCAN_TOKEN+x} ]; then
-          make -C contrib/wurfl
-          curl -s "https://scan.coverity.com/scripts/travisci_build_coverity_scan.sh" | bash || true
-        fi
-    name: Coverity scan | openssl-1.1.1
   - os: linux
     if: type == cron
     compiler: clang