Remove 1_boolean_logic/ sub-dirs.

books/nand2tetris/projects/1_boolean_logic/(*/*.hdl -> *.hdl)
	-Remove the superfluous sub-directories inside
	`1_boolean_logic/`, initially added because I committed `.tst`,
	`.out`, and `.cmp` files in addition to actual `.hdl`
	implementations.
Remove 2_boolean_arithmetic/ sub-dirs.

books/nand2tetris/projects/2_boolean_arithmetic/ALU.hdl
	-Remove `2_boolean_arithmetic/` sub-directories for the same
	reasons delineated in 0dd4a6a.