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/memfile.c

@@ -63,6 +63,7 @@
 #include "nvim/path.h"
 #include "nvim/ui.h"
 #include "nvim/os/os.h"
+#include "nvim/os/input.h"
 
 #define MEMFILE_PAGE_SIZE 4096       /// default page size
 
@@ -455,7 +456,7 @@ int mf_sync(memfile_T *mfp, int flags)
         status = FAIL;
       }
       if (flags & MFS_STOP) {   // Stop when char available now.
-        if (ui_char_avail())
+        if (os_char_avail())
           break;
       } else {
         ui_breakcheck();