travis-ci: Don't use Clang

Currently, there doesn't seem to be a way to configure Travis CI to omit
the Clang build on the coverity/* branches.

See: https://github.com/travis-ci/travis-ci/issues/1975

.travis.yml

@@ -14,10 +14,6 @@ before_script:
 script:
   - if [ "$COVERITY_SCAN_BRANCH" != 1 ]; then make; fi
 
-compiler:
-  - clang
-  - gcc
-
 notifications:
   irc:
     channels:
@@ -28,12 +24,6 @@ notifications:
   email:
     - team@monitoring-plugins.org
 
-# Don't use Clang for Coverity Scan.
-matrix:
-  exclude:
-    - compiler: clang
-      env: COVERITY_SCAN_BRANCH=1
-
 env:
   global:
     # This is the encrypted COVERITY_SCAN_TOKEN, created via the "travis