Remove TypeScript code paths doing language detection based on filename alone

[varungandhi-src]

Flawed APIs:

• getModeFromPath
  • https://github.com/sourcegraph/sourcegraph/pull/58962
  • https://github.com/sourcegraph/sourcegraph/pull/59242
• getFileInfo
  • https://github.com/sourcegraph/sourcegraph/pull/59234

A filename is not sufficient to determine the language. Corresponding go-enry code:

https://sourcegraph.com/github.com/go-enry/go-enry@40f2a1e5b90eec55c20441c2a5911dcfc298a447/-/blob/data/extension.go

The map contains one extension -> a list of languages, not a single language.

The most common example of this in practice is probably .h which is used for both C and C++ headers.