Remove libappindicator support.

Index: CMakeLists.txt
--- CMakeLists.txt.orig
+++ CMakeLists.txt
@@ -21,21 +21,18 @@ configure_file(build-config.h_cmake_in build-config.h)
 find_package(PkgConfig)
 
 pkg_check_modules(gtk3 REQUIRED "gtk+-3.0 >= 2.99.3")
-pkg_check_modules(appindicator3 REQUIRED "appindicator3-0.1 >= 0.4.92")
 pkg_check_modules(xinput REQUIRED "xi >= 1.3")
 pkg_check_modules(x11 REQUIRED x11)
 
 include_directories(
     ${CMAKE_CURRENT_BINARY_DIR}
     ${gtk3_INCLUDE_DIRS}
-    ${appindicator3_INCLUDE_DIRS}
     ${xinput_INCLUDE_DIRS}
     ${x11_INCLUDE_DIRS}
 )
 
 link_directories(
     ${gtk3_LIBRARY_DIRS}
-    ${appindicator3_LIBRARY_DIRS}
     ${xinput_LIBRARY_DIRS}
     ${x11_LIBRARY_DIRS}
 )
@@ -57,7 +54,6 @@ add_executable(${target_name} ${sources})
 
 target_link_libraries(${target_name}
     ${gtk3_LIBRARIES}
-    ${appindicator3_LIBRARIES}
     ${xinput_LIBRARIES}
     ${x11_LIBRARIES}
     -lm