Remove outdated c++ highlighter

Fixes #1652

runtime/syntax/c++.yaml

@@ -1,28 +0,0 @@
-filetype: c++
-
-detect: 
-    filename: "\\.c(c|pp|xx)$|\\.h(h|pp|xx)$|\\.inl$|\\.ii?$|\\.(def)$"
-
-rules:
-    - identifier: "\\b[A-Z_][0-9A-Z_]+\\b"
-    - type: "\\b(auto|float|double|bool|char|int|short|long|sizeof|enum|void|static|const|constexpr|struct|union|typedef|extern|(un)?signed|inline)\\b"
-    - type: "\\b((s?size)|((u_?)?int(8|16|32|64|ptr)))_t\\b"
-    - statement: "\\b(class|namespace|template|public|protected|private|typename|this|friend|virtual|using|mutable|volatile|register|explicit)\\b"
-    - statement: "\\b(for|if|while|do|else|case|default|switch)\\b"
-    - statement: "\\b(try|throw|catch|operator|new|delete)\\b"
-    - special: "\\b(goto|continue|break|return)\\b"
-    - preproc: "^[[:space:]]*#[[:space:]]*(define|pragma|include|(un|ifn?)def|endif|el(if|se)|if|warning|error)"
-    - constant: "'([^'\\\\]|(\\\\[\"'abfnrtv\\\\]))'|'\\\\(([0-3]?[0-7]{1,2}))'|'\\\\x[0-9A-Fa-f]{1,2}'"
-    - statement: "__attribute__[[:space:]]*\\(\\([^)]*\\)\\)|__(aligned|asm|builtin|hidden|inline|packed|restrict|section|typeof|weak)__"
-    - symbol.operator: "[.:;,+*|=!\\%]|<|>|/|-|&"
-    - symbol.brackets: "[(){}]|\\[|\\]"
-    - constant.number: "\\b[0-9]+\\b|\\b0x[0-9A-Fa-f]+\\b"
-    - constant.bool: "\\b(true|false)\\b|NULL"
-    - constant.string: "\"(\\\\.|[^\"])*\""
-    - comment: "//.*"
-    - comment:
-        start: "/\\*"
-        end: "\\*/"
-        rules: []
-
-    - indent-char.whitespace: "[[:space:]]+$"