get rid of the ASAN travis build

Now it's broken even in the old deprecated Ubuntu system, I can't get
it to work and I'm tired of fighting it. With the valgrind build there's
not much point anyway. Feel free to get it to work if you know how.

(cherry picked from commit a24d282)

.travis.yml

@@ -2,19 +2,12 @@ language: cpp
 
 script:
   - |
-        if test "$BUILD_TYPE" = "asan"; then
-            sudo add-apt-repository ppa:litenstein/backports -y
-            sudo apt-get update -q
-            sudo apt-get install libzstd1-dev -y
-        fi
   - ./autogen.sh
   - ./configure --prefix=$PWD/_inst
   - make -s -j $(getconf _NPROCESSORS_ONLN)
   - |
         if test "$TRAVIS_OS_NAME" = "linux"; then
-            if test "$BUILD_TYPE" != "asan"; then # asan uses old version of Ubuntu
-                strict="-strict"
-            fi
+            strict="-strict"
             if test -n "$VALGRIND"; then
                 # See tests/README.
                 sudo /sbin/setcap cap_sys_chroot+ep /usr/lib/valgrind/memcheck-amd64-linux
@@ -60,29 +53,6 @@ matrix:
     compiler: clang
     env: VALGRIND=1
     dist: xenial
-  - os: linux
-    sudo: true # for setcap so we can run the tests in chroot.
-    compiler: clang
-    env: BUILD_TYPE=asan
-    dist: trusty
-    # Sanitizer builds with newer travis fail for unknown reason without giving any message.
-    group: deprecated-2017Q4
-    # And this old version doesn't have zstd, so get it explicitly.
-    addons:
-      apt:
-        packages:
-        - gcc
-        - clang
-        - libcap-ng-dev
-        - libcap-ng-utils
-        - liblzo2-dev
-        - docbook2x
-        - realpath
-        - gdb
-        - valgrind
-        - libarchive-dev
-        - expect
-        - telnet
   - os: linux
     sudo: true # for setcap so we can run the tests in chroot.
     compiler: clang
@@ -91,14 +61,6 @@ matrix:
   allow_failures:
 
 before_script:
-  - |
-     if [ "$BUILD_TYPE" == "asan" ]; then
-         export SAN_FLAGS="-fsanitize=address,leak -fsanitize-address-use-after-scope -fno-omit-frame-pointer"
-     fi
-  - |
-     if [ "$BUILD_TYPE" == "msan" ]; then
-         export SAN_FLAGS="-fsanitize=memory -fno-omit-frame-pointer"
-     fi
   - |
      if [ "$BUILD_TYPE" == "ubsan" ]; then
          export SAN_FLAGS="-fsanitize=undefined -fno-omit-frame-pointer"