Remove specific errors for very old obsolete syntax

Replaces existing tests for removed obsolete-syntax errors with tests
for the resulting regular errors, adds a test for each of the removed
parser errors to make sure that obsolete forms don't start working
again, removes some obsolete/superfluous tests that were now failing.

Deletes some amount of dead code in the parser, also includes some small
changes to parser error messages to accomodate new tests.