patch 8.1.0039: cannot easily delete lines in another buffer

Problem:    Cannot easily delete lines in another buffer.
Solution:   Add deletebufline().
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 1c56bf3..ead6b89 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -2110,6 +2110,8 @@
 cursor({list})			Number	move cursor to position in {list}
 deepcopy({expr} [, {noref}])	any	make a full copy of {expr}
 delete({fname} [, {flags}])	Number	delete the file or directory {fname}
+deletebufline({expr}, {first}[, {last}])
+				Number	delete lines from buffer {expr}
 did_filetype()			Number	|TRUE| if FileType autocmd event used
 diff_filler({lnum})		Number	diff filler lines about {lnum}
 diff_hlID({lnum}, {col})	Number	diff highlighting at {lnum}/{col}
@@ -3517,8 +3519,19 @@
 		successful and -1 when the deletion failed or partly failed.
 
 		Use |remove()| to delete an item from a |List|.
-		To delete a line from the buffer use |:delete|.  Use |:exe|
-		when the line number is in a variable.
+		To delete a line from the buffer use |:delete| or
+		|deletebufline()|.
+
+deletebufline({expr}, {first}[, {last}])		*deletebufline()*
+		Delete lines {first} to {last} (inclusive) from buffer {expr}.
+		If {last} is omitted then delete line {first} only.
+		On success 0 is returned, on failure 1 is returned.
+
+		For the use of {expr}, see |bufname()| above.
+
+		{first} and {last} are used like with |setline()|. Note that
+		when using |line()| this refers to the current buffer. Use "$"
+		to refer to the last line in buffer {expr}.
 
 							*did_filetype()*
 did_filetype()	Returns |TRUE| when autocommands are being executed and the