MDL-70314 lib: Remove a few more hidden files and add instructions

lib/phpspreadsheet/readme_moodle.txt

@@ -24,7 +24,8 @@ CHANGES:
    - vendor/phpoffice/phpspreadsheet/docs
    - vendor/phpoffice/phpspreadsheet/samples
 
-* Remove the hidden folders and files in vendor/phpoffice/phpspreadsheet/:
+* Remove all the hidden folders and files in vendor/phpoffice/phpspreadsheet/ (find . -name ".*"):
+  - .DS_Store
   - .gitattributes
   - .gitignore
   - .php_cs.dist
@@ -32,6 +33,9 @@ CHANGES:
   - .scrutinizer.yml
   - .travis.yml
   - .phpcs.xml.dist
+  - vendor/psr/simple-cache/.editorconfig
+  - vendor/psr/http-factory/.gitignore
+  - vendor/psr/http-factory/.pullapprove.yml
 
  * Add the next Moodle hack at the beginning of the function sysGetTempDir()
 located in vendor/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Shared/File.php

lib/phpspreadsheet/vendor/psr/http-factory/.gitignore

@@ -1,2 +0,0 @@
-composer.lock
-vendor/

lib/phpspreadsheet/vendor/psr/http-factory/.pullapprove.yml

@@ -1,7 +0,0 @@
-extends: default
-reviewers:
-    -
-        name: contributors
-        required: 1
-        teams:
-            - http-factory-contributors

lib/phpspreadsheet/vendor/psr/simple-cache/.editorconfig

@@ -1,12 +0,0 @@
-; This file is for unifying the coding style for different editors and IDEs.
-; More information at http://editorconfig.org
-
-root = true
-
-[*]
-charset = utf-8
-indent_size = 4
-indent_style = space
-end_of_line = lf
-insert_final_newline = true
-trim_trailing_whitespace = true