Apple2: Make 80-columns support dynamic on apple2 target

Add a machinetype identifier to help us quickly identify
Apple //e (bit 7) and //e enhanced (bit 6).

Use it in conio functions for 80-columns code instead of
relying entirely on the __APPLE2ENH__ target.

Move videomode() to the apple2 target, and have it return
an error if 80-columns hardware is not available - this
is a lie for now, it is considered available on //e enhanced,
which may not be true, and not available on //e, which
may also be not true. An ulterior patch will make that
check correctly.

Adapt the box/line drawing characters so that one can use
MouseText on the apple2 target if it is available, by
defining DYN_DRAW_BOX. No change by default: MouseText is
considered available on apple2enh and not available on
apple2.

include/apple2enh.h

@@ -57,18 +57,6 @@
 #define CH_CURS_UP      0x0B
 #define CH_CURS_DOWN    0x0A
 
-#define CH_HLINE        0x5F
-#define CH_VLINE        0xDF
-#define CH_ULCORNER     0x5F
-#define CH_URCORNER     0x20
-#define CH_LLCORNER     0xD4
-#define CH_LRCORNER     0xDF
-#define CH_TTEE         0x5F
-#define CH_BTEE         0xD4
-#define CH_LTEE         0xD4
-#define CH_RTEE         0xDF
-#define CH_CROSS        0xD4
-
 /* These are defined to be OpenApple + NumberKey */
 #define CH_F1   0xB1
 #define CH_F2   0xB2
@@ -81,12 +69,6 @@
 #define CH_F9   0xB9
 #define CH_F10  0xB0
 
-/* Video modes */
-#define VIDEOMODE_40x24     0x15
-#define VIDEOMODE_80x24     0x00
-#define VIDEOMODE_40COL     VIDEOMODE_40x24
-#define VIDEOMODE_80COL     VIDEOMODE_80x24
-
 
 
 /*****************************************************************************/
@@ -112,11 +94,6 @@ extern void a2e_lo_tgi[];
 
 
 
-unsigned __fastcall__ videomode (unsigned mode);
-/* Set the video mode, return the old mode. Call with one of the VIDEOMODE_xx
-** constants.
-*/
-
 void waitvsync (void);
 /* Wait for start of next frame */