Remove check compilation guards from travis build

With the increase in depends testing for PSA changes introduced
here the Travis builds are now taking too long. The check for
compilation guards will only be run on Jenkins now. See this comment
for further details.

https://github.com/ARMmbed/mbedtls/pull/3585#discussion_r485189748

Signed-off-by: John Durkop <john.durkop@fermatsoftware.com>

.travis.yml

@@ -28,10 +28,6 @@ jobs:
       script:
         - tests/scripts/all.sh -k test_full_cmake_gcc_asan
 
-    - name: check compilation guards
-      script:
-        - tests/scripts/all.sh -k 'test_depends_*' 'build_key_exchanges'
-
     - name: macOS
       os: osx
       compiler: clang