Exclude vendor directory from linting

It seems to be excluded already when you run the lint.sh script, but in VS Code
when setting Lint on Save to package it would still lint a file in gocui when
you save it, which is annoying. (Remove the other paths that were there before;
they seem to be unused, and they were added by the auto-migration.)

Unfortunately, gopls will still lint gocui files with its builtin staticcheck
linter, and I couldn't find a way to turn this off. This might be a reason to
turn off staticcheck in gopls (not sure yet).

.golangci.yml

@@ -99,9 +99,7 @@ linters:
       - legacy
       - std-error-handling
     paths:
-      - third_party$
-      - builtin$
-      - examples$
+      - vendor/
 formatters:
   enable:
     - gofumpt
@@ -109,6 +107,4 @@ formatters:
   exclusions:
     generated: lax
     paths:
-      - third_party$
-      - builtin$
-      - examples$
+      - vendor/