Remove the SVG parsing "generic error" reporting special case

With most error-reporting sites switched to using non-generic errors, the
workaround for the generic error message can be removed - giving all messages
a similar structure ("<context>: <message>").

BUG=231612

Review URL: https://codereview.chromium.org/1668183002

Cr-Commit-Position: refs/heads/master@{#373941}
2 files changed