Remove control+r handling from geliboot's pwgets()

pwgets() is based on ngets() from libstand, which includes a feature
that is not wanted in a very of the function designed for password
handling.

Pressing control+r echos out the entered string

This commit removes that feature from pwgets()

PR:		217298
Reported by:	ehaupt
Reviewed by:	kristof, tsoome, ehaupt
Sponsored by:	ScaleEngine Inc.
Differential Revision:	https://reviews.freebsd.org/D9782

sys/boot/geli/pwgets.c

@@ -60,14 +60,6 @@ pwgets(char *buf, int n)
 		putchar('\b');
 	    }
 	    break;
-	case 'r'&037: {
-	    char *p;
-
-	    putchar('\n');
-	    for (p = buf; p < lp; ++p)
-		putchar(*p);
-	    break;
-	}
 	case 'u'&037:
 	case 'w'&037:
 	    lp = buf;