Remove 'ttyfast'

refs #1045 #1051

This was enabled by default a while ago (#1051), and has apparently not
created any issues.  The amount of actual code related to it is tiny, so
it has been removed.

src/nvim/option.c

@@ -1583,9 +1583,6 @@ static vimoption_T
   {"ttybuiltin",  "tbi",  P_BOOL|P_VI_DEF,
    (char_u *)&p_tbi, PV_NONE,
    {(char_u *)TRUE, (char_u *)0L} SCRIPTID_INIT},
-  {"ttyfast",     "tf",   P_BOOL|P_NO_MKRC|P_VI_DEF,
-   (char_u *)&p_tf, PV_NONE,
-   {(char_u *)TRUE, (char_u *)0L} SCRIPTID_INIT},
   {"ttymouse",    "ttym", P_STRING|P_NODEFAULT|P_NO_MKRC|P_VI_DEF,
 #if defined(FEAT_MOUSE) && defined(UNIX)
    (char_u *)&p_ttym, PV_NONE,

src/nvim/option_defs.h

@@ -569,7 +569,6 @@ EXTERN char_u   *p_tsr;         /* 'thesaurus' */
 EXTERN int p_ttimeout;          /* 'ttimeout' */
 EXTERN long p_ttm;              /* 'ttimeoutlen' */
 EXTERN int p_tbi;               /* 'ttybuiltin' */
-EXTERN int p_tf;                /* 'ttyfast' */
 EXTERN long p_ttyscroll;        /* 'ttyscroll' */
 #if defined(FEAT_MOUSE) && defined(UNIX)
 EXTERN char_u   *p_ttym;        /* 'ttymouse' */

src/nvim/screen.c

@@ -4196,8 +4196,7 @@ win_line (
          * Don't do this for double-width characters.
          * Don't do this for a window not at the right screen border.
          */
-        if (p_tf
-            && !(has_mbyte
+        if (!(has_mbyte
                  && ((*mb_off2cells)(LineOffset[screen_row],
                                      LineOffset[screen_row] + screen_Columns)
                      == 2
@@ -7102,8 +7101,9 @@ static int win_do_lines(win_T *wp, int row, int line_count, int mayclear, int de
     return retval;
   }
 
-  if (wp->w_next != NULL && p_tf)   /* don't delete/insert on fast terminal */
+  if (wp->w_next != NULL) {
     return FAIL;
+  }
 
   return MAYBE;
 }