travis: there is only one SSL lib

.travis.yml

 language: cpp
-env:
-  matrix:
-    - SSL_LIB=openssl
 compiler:
   - clang
   - gcc
@@ -33,10 +30,10 @@ before_install:
   - cmake --version
 before_script:
   # First build external lib
-  - if [ "$SSL_LIB" = "openssl" ]; then ./ci/build_openssl.sh; fi
+  - ./ci/build_openssl.sh
   # configure ngtcp2
   - autoreconf -i
-  - if [ "$SSL_LIB" = "openssl" ]; then ./configure --enable-werror PKG_CONFIG_PATH=$PWD/../openssl/build/lib/pkgconfig LDFLAGS="-Wl,-rpath,$PWD/openssl/build/lib"; fi
+  - ./configure --enable-werror PKG_CONFIG_PATH=$PWD/../openssl/build/lib/pkgconfig LDFLAGS="-Wl,-rpath,$PWD/openssl/build/lib"
 script:
   # Now build ngtcp2
   - make check