Deprecate go-remove-unused-imports

Most people use goimports or LSP, which provide more robust alternatives
to parsing compiler errors. In fact, the function doesn't work for newer
versions of Go because the format of the error has changed.

Author: dominikh

README.md

@@ -32,8 +32,6 @@ the following extra features to provide an improved experience:
     `C-c C-f i`)
   - A function for adding imports, including tab completion
     (`go-import-add`, bound to `C-c C-a`)
-  - A function for removing or commenting unused imports
-    (`go-remove-unused-imports`)
   - It is recommended that you use `goimports` or the
     `organize-imports` feature of `gopls` to manage
     adding/removing/organizing imports automatically.

go-mode.el

@@ -544,7 +544,6 @@ statements."
     ["Jump to Definition"    godef-jump t]
     "---"
     ["Add Import"            go-import-add t]
-    ["Remove Unused Imports" go-remove-unused-imports t]
     ["Go to Imports"         go-goto-imports t]
     "---"
     ("Playground"
@@ -1739,7 +1738,6 @@ The following extra functions are defined:
 - `gofmt'
 - `godoc' and `godoc-at-point'
 - `go-import-add'
-- `go-remove-unused-imports'
 - `go-goto-arguments'
 - `go-goto-docstring'
 - `go-goto-function'
@@ -2293,6 +2291,7 @@ If IGNORE-CASE is non-nil, the comparison is case-insensitive."
   "Remove all unused imports.
 If ARG is non-nil, unused imports will be commented, otherwise
 they will be removed completely."
+  (declare (obsolete "set `gofmt-command' to goimports instead, or use LSP and gopls's \"Organize Imports\" code action." "1.7.0"))
   (interactive "P")
   (save-excursion
     (let ((cur-buffer (current-buffer)) flymake-state lines)