Revert "Atari 8-bit MegaCart (bank-switched) cartridge support (#272)"

This reverts commit 9ed41b1.

This failed to build in CI.

Author: mysterymath

mos-platform/CMakeLists.txt

@@ -53,7 +53,6 @@ add_subdirectory(atari8-common)
 add_subdirectory(atari8-dos)
 add_subdirectory(atari8-stdcart)
 add_subdirectory(atari8-xegs)
-add_subdirectory(atari8-mega)
 add_subdirectory(commodore)
 add_subdirectory(c64)
 add_subdirectory(c128)