Suppress warning in isearchb about iswitchb being obsolete

* lisp/isearchb.el (obsolete): Suppress warning about package
being obsolete.  Instead, this has been reported to the bug
tracker, because it requires a rewrite of isearchb.
1 job for master in 90 minutes and 2 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
failed #2246
test-all

01:30:02

 
Name Stage Failure
failed
test-all Test The script exceeded the maximum execution time set for the job
  ELC      lisp/progmodes/xref-tests.elc
GEN lisp/progmodes/xref-tests.log
ELC lisp/ps-print-tests.elc
GEN lisp/ps-print-tests.log
ELC lisp/register-tests.elc
GEN lisp/register-tests.log
ELC lisp/replace-tests.elc
Pulling docker image gitlab/gitlab-runner-helper:x86_64-f100a208 ...
ERROR: Job failed: execution took longer than 1h30m0s seconds