Remove textLength as a global SVG attribute

It can only be used on SVG <text>, <tspan>, and <textPath>, and
previously <tref> which has been removed now.

svg/global_attributes.json

@@ -547,42 +547,6 @@
  }
  }
  },
- "textLength": {
- "__compat": {
- "mdn_url": "https://developer.mozilla.org/docs/Web/SVG/Attribute/textLength",
- "spec_url": "https://svgwg.org/svg2-draft/text.html#TextElementTextLengthAttribute",
- "support": {
- "chrome": {
- "version_added": true
- },
- "chrome_android": "mirror",
- "edge": {
- "version_added": "12"
- },
- "firefox": {
- "version_added": true
- },
- "firefox_android": "mirror",
- "ie": {
- "version_added": "11"
- },
- "oculus": "mirror",
- "opera": "mirror",
- "opera_android": "mirror",
- "safari": {
- "version_added": true
- },
- "safari_ios": "mirror",
- "samsunginternet_android": "mirror",
- "webview_android": "mirror"
- },
- "status": {
- "experimental": false,
- "standard_track": true,
- "deprecated": false
- }
- }
- },
  "class": {
  "__compat": {
  "mdn_url": "https://developer.mozilla.org/docs/Web/SVG/Attribute/class",