Remove raw chainspecs from master branch

Title was changed from

Refac network features and embeded runtimes

to

Remove raw chainspecs from master branch

After the comments below.

---

Currently the feature gdev has two meanings:

• the runtime to build is gdev
• the node should embed hexadecimal-text-encoded chainspecs defined in a gdev-raw.json file

// Hardcoded raw chainspecs with previously generated values, resulting in a needlessly heavy binary due to hexadecimal-text-encoded values.
#[cfg(feature = "gdev")]
"gdev" => Box::new(chain_spec::gdev::ChainSpec::from_json_bytes(
    &include_bytes!("../specs/gdev-raw.json")[..],
)?),

This would be convenient to split this into two features as suggested for gtest:

// Return hardcoded live chainspecs, only with the embed feature enabled.
// Embed client spec and genesis to avoid embedding hexadecimal runtime
// and having hexadecimal runtime in the git history.
// This will only build on a branch that has a file named ./node/specs/gtest-raw.json.
#[cfg(all(feature = "gtest", feature = "embed"))]
"gtest" => Box::new(chain_spec::gtest::ChainSpec::from_json_bytes(
    &include_bytes!("../specs/gtest-raw.json")[..],
)?),

Advantages would be:

• no need to commit raw chainspecs on master to be able to build with gdev feature
• embed feature reserved for network branches which is the only place where raw chainspecs are relevant, and only for a given network

Additionally, the cbor format could be used instead of json to decrease size (TODO measurements). Doing this would require a tool to edit client spec part of chainspecs because it would not be possible to edit manually anymore.