Drop unused travis CI configuration files

11 jobs for travis-ci-cleanup in 9 minutes and 50 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #5630806
build:cmake

00:05:01

passed #5630803
build:debug

00:09:25

manual #5630808
allowed to fail manual
build:i686-w64-mingw32-cmake
passed #5630807
build:i686-w64-mingw32-debug

00:05:49

manual #5630805
allowed to fail manual
build:legacy
passed #5630802
build:production

00:06:18

manual #5630804
allowed to fail manual
build:reduced
manual #5630811
allowed to fail manual
build:stretch
passed #5630809
build:x86_64-w64-mingw32

00:04:52

passed #5630810
build:x86_64-w64-mingw32-cmake-debug

00:09:48

manual #5630812
allowed to fail manual
build:xenial