ui: Remove ui_inchar/ui_char_avail

Also:

- Remove NO_CONSOLE_INPUT/NO_CONSULE preprocessor conditionals
- Remove ctrl_c_interrupts variable, check for mapped_ctrl_c directly in
  process_interrupts()
- Move ui_inchar profiling to input_poll which is where Nvim blocks for input.

src/nvim/globals.h

@@ -855,7 +855,6 @@ EXTERN char_u   *exe_name;              /* the name of the executable */
 EXTERN int dont_scroll INIT(= FALSE);     /* don't use scrollbars when TRUE */
 #endif
 EXTERN int mapped_ctrl_c INIT(= FALSE);      /* CTRL-C is mapped */
-EXTERN bool ctrl_c_interrupts INIT(= true);  /* CTRL-C sets got_int */
 
 EXTERN cmdmod_T cmdmod;                 /* Ex command modifiers */