Travis: Drop support for coverity_scan, we do not use it

The UX is pretty bad, and the fact that all reports are private by
default with no option to make them public makes Coverity Scan hardly
usable in a community-driven project.

.travis.yml

@@ -47,15 +47,6 @@ matrix:
             - &linux_deps [libasound2-dev, libgl1-mesa-dev, libglu1-mesa-dev, libx11-dev, libxcursor-dev, libxi-dev, libxinerama-dev, libxrandr-dev]
             - &linux_mono_deps [mono-devel, msbuild, nuget]
 
-        coverity_scan:
-          project:
-            name: "godotengine/godot"
-            description: "Godot Engine Coverity scans"
-          notification_email: [email protected]
-          build_command_prepend: ""
-          build_command: "scons p=x11 -j2 $OPTIONS"
-          branch_pattern: coverity_scan
-
     - name: Linux export template (release, Clang)
       stage: build
       env: PLATFORM=x11 TOOLS=no TARGET=release CACHE_NAME=${PLATFORM}-clang EXTRA_ARGS="warnings=extra werror=yes"