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/misc1.c

@@ -58,6 +58,7 @@
 #include "nvim/window.h"
 #include "nvim/os/os.h"
 #include "nvim/os/shell.h"
+#include "nvim/os/input.h"
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "misc1.c.generated.h"
@@ -2383,7 +2384,7 @@ int get_keystroke(void)
 
     /* First time: blocking wait.  Second time: wait up to 100ms for a
      * terminal code to complete. */
-    n = ui_inchar(buf + len, maxlen, len == 0 ? -1L : 100L, 0);
+    n = os_inchar(buf + len, maxlen, len == 0 ? -1L : 100L, 0);
     if (n > 0) {
       /* Replace zero and CSI by a special key code. */
       n = fix_input_buffer(buf + len, n, FALSE);