Remove remnants from the compile-time multi-monitor support

When the logic to use a setting to decide between RandR and xinerama
apparently the variable in config.mk and the travis tests were never
removed.

.travis.yml

@@ -19,10 +19,6 @@ script: make && make test
 compiler:
     - gcc
     - clang
-env:
-  - MULTIMON=xrandr
-  - MULTIMON=xinerama
-  - MULTIMON=none
 notifications:
     irc:
         channels:

config.mk

@@ -7,15 +7,6 @@ ifneq ($(wildcard ./.git/.),)
 VERSION := $(shell git describe --tags)
 endif
 
-# Specifies which X extension dunst should use for multi monitor support
-# Possible values are randr, xinerama or none
-# * xrandr is the recommended/default value and should be the best option in most cases
-# * xinerama is the legacy equivalent to randr but does not support some more
-#   advanced features like per-monitor dpi calculation it should probably one
-#   be used if xrandr cannot be used for some reason.
-# * none disables multi-monitor support and dunst will assume only one monitor.
-MULTIMON ?= xrandr
-
 # uncomment to disable parsing of dunstrc
 # or use "CFLAGS=-DSTATIC_CONFIG make" to build
 #STATIC= -DSTATIC_CONFIG