Remove unnecessary CMake modules.

* Compiling without find_package(OpenGL REQUIRED) has no side-effect because LOVE uses SDL to load OpenGL. GLAD is used to as substitute for OpenGL headers too.
* Mpg123 is no longer used in LOVE 12. Remove the respective CMake module.
* CMake has its own FindOpenAL.cmake script. There's no need to provide our own.

CMakeLists.txt

@@ -183,7 +183,6 @@ Please see https://github.com/love2d/megasource
 	find_package(Harfbuzz REQUIRED)
 	find_package(ModPlug REQUIRED)
 	find_package(OpenAL REQUIRED)
-	find_package(OpenGL REQUIRED)
 	find_package(SDL2 2.0.9 REQUIRED CONFIG COMPONENTS SDL2main)
 	find_package(Theora REQUIRED)
 	find_package(Vorbis REQUIRED)
@@ -206,7 +205,6 @@ Please see https://github.com/love2d/megasource
 	)
 
 	set(LOVE_LINK_LIBRARIES
-		${OPENGL_gl_LIBRARY}
 		${SDL2_LIBRARIES}
 		${FREETYPE_LIBRARY}
 		${HARFBUZZ_LIBRARY}

extra/cmake/FindMPG123.cmake

@@ -1,25 +0,0 @@
-# Sets the following variables:
-#
-# MPG123_FOUND
-# MPG123_INCLUDE_DIR
-# MPG123_LIBRARY
-
-set(MPG123_SEARCH_PATHS
-	/usr/local
-	/usr
-	)
-
-find_path(MPG123_INCLUDE_DIR
-	NAMES mpg123.h
-	PATH_SUFFIXES include
-	PATHS ${MPG123_SEARCH_PATHS})
-
-find_library(MPG123_LIBRARY
-	NAMES mpg123
-	PATH_SUFFIXES lib
-	PATHS ${MPG123_SEARCH_PATHS})
-
-include(FindPackageHandleStandardArgs)
-find_package_handle_standard_args(MPG123 DEFAULT_MSG MPG123_LIBRARY MPG123_INCLUDE_DIR)
-
-mark_as_advanced(MPG123_INCLUDE_DIR MPG123_LIBRARY)

extra/cmake/FindOpenAL.cmake

@@ -1,28 +0,0 @@
-# FindOpenAL.cmake that comes with CMake expects "#include <al.h>" to be used
-# However, we use "#include <AL/al.h>"
-
-# Sets the following variables:
-#
-# OPENAL_FOUND
-# OPENAL_INCLUDE_DIR
-# OPENAL_LIBRARY
-
-set(OPENAL_SEARCH_PATHS
-	/usr/local
-	/usr
-	)
-
-find_path(OPENAL_INCLUDE_DIR
-	NAMES AL/al.h
-	PATH_SUFFIXES include
-	PATHS ${OPENAL_SEARCH_PATHS})
-
-find_library(OPENAL_LIBRARY
-	NAMES openal
-	PATH_SUFFIXES lib
-	PATHS ${OPENAL_SEARCH_PATHS})
-
-include(FindPackageHandleStandardArgs)
-find_package_handle_standard_args(OpenAL DEFAULT_MSG OPENAL_LIBRARY OPENAL_INCLUDE_DIR)
-
-mark_as_advanced(OPENAL_INCLUDE_DIR OPENAL_LIBRARY)