Disable usbsan.

It presently fails like this:

    /usr/bin/ld: unrecognized option '--push-state--no-as-needed'
    /usr/bin/ld: use the --help option for usage information
    collect2: error: ld returned 1 exit status
        "g++-7"    -o "../../bin.v2/libs/program_options/test/gcc-7/debug/cxxstd-03-iso/link-static/test_convert"
       -Wl,--start-group
        "../../bin.v2/libs/program_options/test/gcc-7/debug/cxxstd-03-iso/link-static/test_convert.o"
        "../../bin.v2/libs/program_options/build/gcc-7/debug/cxxstd-03-iso/link-static/libboost_program_options.a"
       -Wl,-Bstatic  -Wl,-Bdynamic  -Wl,--end-group -m64 -std=c++03 -g -fno-sanitize-recover=undefined -fsanitize=undefined

This error seems like some misconfiguration of compiler install, not something I can fix.

.travis.yml

@@ -114,21 +114,6 @@ jobs:
       script:
         - libs/$SELF/ci/cppcheck.sh
 
-    - os: linux
-      env:
-        - COMMENT=UBSAN
-        - B2_VARIANT=variant=debug
-        - TOOLSET=gcc-7
-        - CXXFLAGS="cxxflags=-fno-omit-frame-pointer cxxflags=-fsanitize=undefined cxxflags=-fno-sanitize-recover=undefined"
-        - LINKFLAGS="linkflags=-fsanitize=undefined linkflags=-fno-sanitize-recover=undefined"
-        - UBSAN_OPTIONS=print_stacktrace=1
-      addons:
-        apt:
-          packages:
-            - g++-7
-          sources:
-            - ubuntu-toolchain-r-test
-
     - os: linux
       env: 
         - COMMENT=CodeCov