Disallow field licenseText for npm

What does this MR do and why?

Describe in detail what your merge request does and why.

This MR disallows the licenseText field in a npm package's meta-data

Consider the following use case:

• package.json includes a field license
• the value of license is an SPDX license identifier (see https://docs.npmjs.com/cli/v8/configuring-npm/package-json#license)
• you publish the package with yarn

Upon publishing with npm, things are fine.
Upon publishing with yarn, the SPDX id from license is used to add the licenseText field and populate it with the contents as per https://spdx.org/licenses/

Since the license's content is (very) large, this is resulting in a Package json structure is too large error.

Relates to #345759 (closed)

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