The bufmode_t enum was added to src/support/ios.h in d316c93 by Jeff Bezanson with the comment

// this flag controls when data actually moves out to the underlying I/O
// channel. memory streams are a special case of this where the data
// never moves out.
typedef enum { bm_none, bm_line, bm_block, bm_mem } bufmode_t;

In 30aed86 Keno Fischer added a new comment and modified the enum:

 // this flag controls when data actually moves out to the underlying I/O
 // channel. memory streams are a special case of this where the data
 // never moves out.
-typedef enum { bm_none, bm_line, bm_block, bm_mem } bufmode_t;
+
+//make it compatible with UV Handles
+typedef enum { bm_none=UV_HANDLE_TYPE_MAX+1, bm_line, bm_block, bm_mem } bufmode_t;

In c12aca8 Jameson Nash removed uv.h and updated the enum definition to no longer use UV_HANDLE_TYPE_MAX:

-typedef enum { bm_none=UV_HANDLE_TYPE_MAX+1, bm_line, bm_block, bm_mem } bufmode_t;
+typedef enum { bm_none=1000, bm_line, bm_block, bm_mem } bufmode_t;

This last change made the comment by Keno Fischer seemingly obsolete, yet the comment remains. This pull request simply removes the two lines remaining from Keno Fischer's commit. Perhaps it is better to update the comment to explain why bm_none now has the value 1000 but I did not dig deep enough into the changes to figure out if this value is significant in some way that should be documented.