travis: remove the ngtcp2+gnutls build

it permafails right now and I don't know why

Avoids #6493

.travis.yml

@@ -137,27 +137,6 @@ jobs:
         - libpsl-dev
         - libbrotli-dev
         - libzstd-dev
-  - env:
-    - T=novalgrind NGTCP2=yes GNUTLS=yes C="PKG_CONFIG_PATH=$HOME/ngbuild --without-ssl --with-gnutls=$HOME/ngbuild --with-ngtcp2=$HOME/ngbuild --with-nghttp3=$HOME/ngbuild" NOTESTS=
-    - OVERRIDE_CC="CC=gcc-8" OVERRIDE_CXX="CXX=g++-8"
-    addons:
-      apt:
-        <<: *common_apt
-        packages:
-        - *common_packages
-        - libpsl-dev
-        - libbrotli-dev
-        - libzstd-dev
-        - autogen
-        - automake
-        - autopoint
-        - bison
-        - gperf
-        - libgmp-dev
-        - libopts25-dev
-        - libp11-kit-dev
-        - libtasn1-6-dev
-        - nettle-dev
   - env:
     - T=debug-wolfssl C="--with-wolfssl --without-ssl"
     - OVERRIDE_CC="CC=gcc-8" OVERRIDE_CXX="CXX=g++-8"