[ci] Remove --coverage as use of --enable-code-coverage

.travis.yml

@@ -6,9 +6,8 @@ language: cpp
 env:
   global:
     - CPPFLAGS=""
-    - CFLAGS="-Werror -Werror=unused-function --coverage"
-    - CXXFLAGS="-Werror -Werror=unused-function -Wno-deprecated-register --coverage" # glib uses register and clang raises a warning
-    - LDFLAGS="--coverage"
+    - CFLAGS="-Werror -Werror=unused-function"
+    - CXXFLAGS="-Werror -Werror=unused-function -Wno-deprecated-register" # glib uses register and clang raises a warning
     - CONFIGURE_OPTS="--with-freetype --with-glib --with-gobject --with-cairo --with-icu --with-graphite2"
     - NOCONFIGURE=1
     # COVERITY_SCAN_TOKEN