Remove or deprecate exported names ending in `_`

[cpcallen]

Background

During the first pass converting goog.provide to goog.module, we are going export most or all existing exported identifiers, even ones marked @private and ending in underscore (_). This is being done to ensure that the initial conversion does not break other code within our own codebase (as well as in those of Blockly embedders).

Issue

Since:

• it doesn't really make sense to export identifiers that are supposed to be private, and
• we do not want external developers using these not-intended-to-be-public exports.

Suggested fix

We should either:

• remove these exports (where doing does not and is not expected to break anything), or
• mark them as @deprecated and wrapped with a call to the warn method from Blockly.utils.deprecation.

Alternatives considered

Doing nothing, and leaving them exported and not marked for deprecation. This runs the risk of them becoming de-facto parts of the API we need to continue to support in the future.