Update HCL/Terraform grammar to hashicorp/syntax (#6802)

Co-authored-by: Colin Seymour <colin@github.com>

.gitmodules

@@ -191,9 +191,6 @@
 [submodule "vendor/grammars/TXL"]
 	path = vendor/grammars/TXL
 	url = https://github.com/MikeHoffert/Sublime-Text-TXL-syntax
-[submodule "vendor/grammars/Terraform.tmLanguage"]
-	path = vendor/grammars/Terraform.tmLanguage
-	url = https://github.com/alexlouden/Terraform.tmLanguage
 [submodule "vendor/grammars/Textmate-Gosu-Bundle"]
 	path = vendor/grammars/Textmate-Gosu-Bundle
 	url = https://github.com/jpcamara/Textmate-Gosu-Bundle

grammars.yml

@@ -160,8 +160,6 @@ vendor/grammars/TLA:
 - source.tla
 vendor/grammars/TXL:
 - source.txl
-vendor/grammars/Terraform.tmLanguage:
-- source.terraform
 vendor/grammars/Textmate-Gosu-Bundle:
 - source.gosu.2
 vendor/grammars/TypeScript-TmLanguage:

lib/linguist/languages.yml

@@ -2697,7 +2697,7 @@ HCL:
   ace_mode: ruby
   codemirror_mode: ruby
   codemirror_mime_type: text/x-ruby
-  tm_scope: source.terraform
+  tm_scope: source.hcl
   language_id: 144
 HLSL:
   type: programming

vendor/README.md

@@ -227,7 +227,7 @@ This is a list of grammars that Linguist selects to provide syntax highlighting
 - **Groovy:** [textmate/groovy.tmbundle](https://github.com/textmate/groovy.tmbundle)
 - **Groovy Server Pages:** [textmate/java.tmbundle](https://github.com/textmate/java.tmbundle)
 - **HAProxy:** [abulimov/atom-language-haproxy](https://github.com/abulimov/atom-language-haproxy)
-- **HCL:** [alexlouden/Terraform.tmLanguage](https://github.com/alexlouden/Terraform.tmLanguage)
+- **HCL:** [hashicorp/syntax](https://github.com/hashicorp/syntax)
 - **HLSL:** [tgjones/shaders-tmLanguage](https://github.com/tgjones/shaders-tmLanguage)
 - **HOCON:** [jacobwgillespie/language-hocon](https://github.com/jacobwgillespie/language-hocon)
 - **HTML:** [tree-sitter/tree-sitter-html](https://github.com/tree-sitter/tree-sitter-html) 🐌