Syntax:
DROP SPATIAL REFERENCE SYSTEM
    [IF EXISTS]
    srid

srid: 32-bit unsigned integer

This statement removes a spatial reference system (SRS) definition from
the data dictionary. It requires the SUPER privilege.

Example:

DROP SPATIAL REFERENCE SYSTEM 4120;

If no SRS definition with the SRID value exists, an error occurs unless
IF EXISTS is specified. In that case, a warning occurs rather than an
error.

If the SRID value is used by some column in an existing table, an error
occurs. For example:

mysql> DROP SPATIAL REFERENCE SYSTEM 4326;
ERROR 3716 (SR005): Can't modify SRID 4326. There is at
least one column depending on it.

To identify which column or columns use the SRID, use this query:

SELECT * FROM INFORMATION_SCHEMA.ST_GEOMETRY_COLUMNS WHERE SRS_ID=4326;

SRID values must be in the range of 32-bit unsigned integers, with
these restrictions:

o SRID 0 is a valid SRID but cannot be used with DROP SPATIAL REFERENCE
  SYSTEM.

o If the value is in a reserved SRID range, a warning occurs. Reserved
  ranges are [0, 32767] (reserved by EPSG), [60,000,000, 69,999,999]
  (reserved by EPSG), and [2,000,000,000, 2,147,483,647] (reserved by
  MySQL). EPSG stands for the European Petroleum Survey Group
  (http://epsg.org).

o Users should not drop SRSs with SRIDs in the reserved ranges. If
  system-installed SRSs are dropped, the SRS definitions may be
  recreated for MySQL upgrades.

URL: https://dev.mysql.com/doc/refman/8.0/en/drop-spatial-reference-system.html

