Remove conf highlighting (too many conflicts)

Fixes #2031

The conf highlighter interferes with many more specific highlighters and
doesn't provide much value on its own.

runtime/syntax/conf.yaml

@@ -1,17 +0,0 @@
-filetype: conf
-
-detect:
-    filename: "\\.c[o]?nf$"
-
-rules:
-    - constant.string:
-        start: "\""
-        end: "\""
-        skip: "\\\\."
-        rules: []
-
-    - comment:
-        start: "#"
-        end: "$"
-        rules: []
-