We have some excessive and duplicative tests in the travis-ci setup.

This is causing us to run out of travis-ci credits, making tests not run
at all.  I deleted the duplicative tests and then disabled two additonal
ones by commenting them out that would be nice to run but I think are
not essential.  In particular, the OSX one eats up a ton of credits.  So
I disabled that.  Maybe we can turn it back on later if we end up well
under the credit budget (or switch to github actions which appears to
have higher limits)

.travis.yml

@@ -12,15 +12,6 @@ matrix:
       script:
         - dlib/travis/build-and-test.sh
 
-    ###################
-    - language: cpp
-      compiler: clang
-      os: linux
-      env:
-        - VARIANT=examples-debug
-      script:
-        - dlib/travis/build-and-test.sh
-
     ###################
     - language: cpp
       compiler: gcc
@@ -31,15 +22,6 @@ matrix:
       script:
         - dlib/travis/build-and-test.sh
 
-    ###################
-    - language: cpp
-      compiler: gcc
-      os: linux
-      env:
-        - VARIANT=tools
-      script:
-        - dlib/travis/build-and-test.sh
-
     ###################
     - language: cpp
       compiler: gcc
@@ -53,15 +35,6 @@ matrix:
       script:
         - dlib/travis/build-and-test.sh
 
-    ###################
-    - language: cpp
-      compiler: gcc
-      os: linux
-      env:
-        - VARIANT=dlib_all_source_cpp
-      script:
-        - dlib/travis/build-and-test.sh
-
     ########### test with C++17 ########
     - language: cpp
       compiler: gcc
@@ -84,21 +57,13 @@ matrix:
         - dlib/travis/build-and-test.sh
 
     ###################
-    - language: cpp
-      compiler: gcc
-      os: linux
-      env:
-        - VARIANT=examples
-      script:
-        - dlib/travis/build-and-test.sh
-
-    ###################
-    - language: python
-      python: 3.5
-      env:
-        - VARIANT=python-api
-      script:
-        - dlib/travis/build-and-test.sh
+    # Disabled to avoid spending too many travis-ci credits each month.
+    #- language: python
+    #  python: 3.5
+    #  env:
+    #    - VARIANT=python-api
+    #  script:
+    #    - dlib/travis/build-and-test.sh
 
     ###################
     - language: python
@@ -109,15 +74,17 @@ matrix:
         - dlib/travis/build-and-test.sh
 
     ###################
-    - language: cpp
-      os: osx
-      osx_image: xcode9.2
-      env:
-        - VARIANT=test
-        # Don't test the timer because it relies on the machine running it not
-        # being under high load, but that seems to be unlikely on the travis
-        # osx VMs.
-        - DISABLED_TESTS="--no_test_timer"
-      script:
-        - dlib/travis/build-and-test.sh
+    # Disabled to avoid spending too many travis-ci credits each month.  They
+    # also charge 5x as many credits for osx as linux.
+    #- language: cpp
+    #  os: osx
+    #  osx_image: xcode9.2
+    #  env:
+    #    - VARIANT=test
+    #    # Don't test the timer because it relies on the machine running it not
+    #    # being under high load, but that seems to be unlikely on the travis
+    #    # osx VMs.
+    #    - DISABLED_TESTS="--no_test_timer"
+    #  script:
+    #    - dlib/travis/build-and-test.sh
 

dlib/travis/build-and-test.sh

@@ -30,20 +30,6 @@ if [ "$VARIANT" = "test-debug" ]; then
   ./dtest --runall $DISABLED_TESTS
 fi
 
-if [ "$VARIANT" = "dlib_all_source_cpp" ]; then
-  mkdir build
-  cd build
-  cmake ../dlib/test -DCMAKE_CXX_FLAGS="${CXX_FLAGS}"
-  cmake --build . --target dlib_all_source_cpp -- -j 2
-fi
-
-if [ "$VARIANT" = "tools" ]; then
-  mkdir build
-  cd build
-  cmake ../dlib/test/tools -DCMAKE_CXX_FLAGS="${CXX_FLAGS}"
-  cmake --build .  -- -j 2
-fi
-
 # The point of this test is just to make sure the cmake scripts work with the
 # oldest version of cmake we are supposed to support.
 if [ "$VARIANT" = "old-cmake" ]; then
@@ -69,20 +55,6 @@ if [ "$VARIANT" = "old-cmake" ]; then
   $CMAKEDIR/2.8/bin/cmake --build .  -- -j 2
 fi
 
-if [ "$VARIANT" = "examples" ]; then
-  mkdir build
-  cd build
-  cmake ../examples -DCMAKE_CXX_FLAGS="${CXX_FLAGS}"
-  cmake --build . -- -j 1
-fi
-
-if [ "$VARIANT" = "examples-debug" ]; then
-  mkdir build
-  cd build
-  cmake ../examples -DDLIB_ENABLE_ASSERTS=1 -DCMAKE_CXX_FLAGS="${CXX_FLAGS}"
-  cmake --build . -- -j 1
-fi
-
 if [ "$VARIANT" = "python-api" ]; then
   python setup.py test --clean
   pip uninstall numpy -y