remove sixel stub code

Remove stub code that was used for an experiment of adding sixel code to st
from the commit f7398434.

st.c

@@ -51,7 +51,6 @@ enum term_mode {
 	MODE_ECHO        = 1 << 4,
 	MODE_PRINT       = 1 << 5,
 	MODE_UTF8        = 1 << 6,
-	MODE_SIXEL       = 1 << 7,
 };
 
 enum cursor_movement {
@@ -78,12 +77,11 @@ enum charset {
 enum escape_state {
 	ESC_START      = 1,
 	ESC_CSI        = 2,
-	ESC_STR        = 4,  /* OSC, PM, APC */
+	ESC_STR        = 4,  /* DCS, OSC, PM, APC */
 	ESC_ALTCHARSET = 8,
 	ESC_STR_END    = 16, /* a final string was encountered */
 	ESC_TEST       = 32, /* Enter in test mode */
 	ESC_UTF8       = 64,
-	ESC_DCS        =128,
 };
 
 typedef struct {
@@ -2090,12 +2088,9 @@ tdectest(char c)
 void
 tstrsequence(uchar c)
 {
-	strreset();
-
 	switch (c) {
 	case 0x90:   /* DCS -- Device Control String */
 		c = 'P';
-		term.esc |= ESC_DCS;
 		break;
 	case 0x9f:   /* APC -- Application Program Command */
 		c = '_';
@@ -2107,6 +2102,7 @@ tstrsequence(uchar c)
 		c = ']';
 		break;
 	}
+	strreset();
 	strescseq.type = c;
 	term.esc |= ESC_STR;
 }
@@ -2304,7 +2300,7 @@ tputc(Rune u)
 	Glyph *gp;
 
 	control = ISCONTROL(u);
-	if (u < 127 || !IS_SET(MODE_UTF8 | MODE_SIXEL)) {
+	if (u < 127 || !IS_SET(MODE_UTF8)) {
 		c[0] = u;
 		width = len = 1;
 	} else {
@@ -2325,23 +2321,11 @@ tputc(Rune u)
 	if (term.esc & ESC_STR) {
 		if (u == '\a' || u == 030 || u == 032 || u == 033 ||
 		   ISCONTROLC1(u)) {
-			term.esc &= ~(ESC_START|ESC_STR|ESC_DCS);
+			term.esc &= ~(ESC_START|ESC_STR);
-			if (IS_SET(MODE_SIXEL)) {
-				/* TODO: render sixel */;
-				term.mode &= ~MODE_SIXEL;
-				return;
-			}
 			term.esc |= ESC_STR_END;
 			goto check_control_code;
 		}
 
-		if (IS_SET(MODE_SIXEL)) {
-			/* TODO: implement sixel mode */
-			return;
-		}
-		if (term.esc&ESC_DCS && strescseq.len == 0 && u == 'q')
-			term.mode |= MODE_SIXEL;
-
 		if (strescseq.len+len >= strescseq.siz) {
 			/*
 			 * Here is a bug in terminals. If the user never sends
@@ -2453,7 +2437,7 @@ twrite(const char *buf, int buflen, int show_ctrl)
 	int n;
 
 	for (n = 0; n < buflen; n += charsize) {
-		if (IS_SET(MODE_UTF8) && !IS_SET(MODE_SIXEL)) {
+		if (IS_SET(MODE_UTF8)) {
 			/* process a complete utf8 char */
 			charsize = utf8decode(buf + n, &u, buflen - n);
 			if (charsize == 0)