Erase correct key in unit test PasswordRAMStoreTest.TooLongPassword

Was attempting to erase the wrong key "key-long" for the test.  It
should be erasing "key-too-long".  Fix this.  Given that that line in
the test was to erase a non-existent key and confirm failure; the test
passed before with the wrong non-existent key, and still passes with the
right non-existent key.  Clearly a cut and paste error as a result of
copying the previous LongPassword test when initially added in:
    c6657aab
    Add unit tests for PasswordRAMStore module (#795617)
4 jobs for whole-fat-warning in 14 minutes and 31 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #355616
centos_build

00:04:50

passed #355617
ubuntu_build

00:03:42

 
  Test
passed #355618
centos_test

00:09:22

passed #355619
ubuntu_test

00:09:40