travis-ci: disable OSX testing

OSX testing completely implemented on local MAC hosts with OSX 14
and 15 versions. So no more need to test and support issues with
testing OSX with 14 version on travis-ci.

Part of #4893

.travis.yml

@@ -8,8 +8,6 @@ language: cpp
 os: linux
 compiler: gcc
 
-osx_image: xcode10.2
-
 cache:
     directories:
       - $HOME/.cache
@@ -28,9 +26,6 @@ jobs:
       - name: "RelWithDebInfo build + test (Linux, clang)"
         env: TARGET=test
         compiler: clang
-      - name: "RelWithDebInfo build + test (OS X Mojave 10.14)"
-        env: TARGET=test
-        os: osx
       - name: "Debug build + test + coverage (Linux, gcc)"
         env: TARGET=coverage