Manifests and tag schema contain duplicate descriptions

[braingram]

Tag descriptions are duplicated in the manifest and schema. Here's an example for time:

asdf-standard/resources/manifests/asdf-format.org/core/core-1.6.0.yaml

Lines 126 to 156 in ed88589

	- tag_uri: tag:stsci.edu:asdf/time/time-1.2.0
	schema_uri: http://stsci.edu/schemas/asdf/time/time-1.2.0
	title: Represents an instance in time.
	description: |-
	A "time" is a single instant in time. It may explicitly specify the
	way time is represented (the "format") and the "scale" which
	specifies the offset and scaling relation of the unit of time.
	Specific emphasis is placed on supporting time scales (e.g. UTC,
	TAI, UT1, TDB) and time representations (e.g. JD, MJD, ISO 8601)
	that are used in astronomy and required to calculate, e.g., sidereal
	times and barycentric corrections.
	Times may be represented as one of the following:
	- an object, with explicit `value`, and optional `format`, `scale`
	and `location`.
	- a string, in which case the format is guessed from across
	the unambiguous options (`iso`, `byear`, `jyear`, `yday`), and the
	scale is hardcoded to `UTC`.
	In either case, a single time tag may be used to represent an
	n-dimensional array of times, using either an `ndarray` tag or
	inline as (possibly nested) YAML lists. If YAML lists, the same
	format must be used for all time values.
	The precision of the numeric formats should only be assumed to be as
	good as an IEEE-754 double precision (float64) value. If
	higher-precision is required, the `iso` or `yday` format should be
	used.

asdf-standard/resources/schemas/stsci.edu/asdf/time/time-1.2.0.yaml

Lines 6 to 33 in ed88589

	description: |
	A "time" is a single instant in time. It may explicitly specify the
	way time is represented (the "format") and the "scale" which
	specifies the offset and scaling relation of the unit of time.
	Specific emphasis is placed on supporting time scales (e.g. UTC,
	TAI, UT1, TDB) and time representations (e.g. JD, MJD, ISO 8601)
	that are used in astronomy and required to calculate, e.g., sidereal
	times and barycentric corrections.
	Times may be represented as one of the following:
	- an object, with explicit `value`, and optional `format`, `scale`
	and `location`.
	- a string, in which case the format is guessed from across
	the unambiguous options (`iso`, `byear`, `jyear`, `yday`), and the
	scale is hardcoded to `UTC`.
	In either case, a single time tag may be used to represent an
	n-dimensional array of times, using either an `ndarray` tag or
	inline as (possibly nested) YAML lists. If YAML lists, the same
	format must be used for all time values.
	The precision of the numeric formats should only be assumed to be as
	good as an IEEE-754 double precision (float64) value. If
	higher-precision is required, the `iso` or `yday` format should be
	used.

This creates the possibility of a non-matching description as these will need to be synchronized manually. Is this duplication necessary?