Resolve doxygen warning in filesystems docs

[kegilbert]

Came up while writing docs for the filesystem APIs that we had class references for all blockdevice classes but ProfilingBlockDevice. @AnotherButler mentioned we had removed filesystems once from the doxygen exclusion list, so looks like we had all but that file generated before it was added back to the exclusion list.

Fixed the one warning we had in doxygen, @sg- was there a reason features/filesystem should be on the exclusion list other than the previous warnings?

[sg-]

Fixed the one warning we had in doxygen, @sg- was there a reason features/filesystem should be on the exclusion list other than the previous warnings?

Nope.

[adbridge]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 368
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/5395/

Triggering tests

/morph test
/morph uvisor-test

[mbed-ci]

Test : SUCCESS

Build number : 180
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/5395/180

[mbed-ci]

Build : SUCCESS

Build number : 392
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/5395/

Triggering tests

/morph test
/morph uvisor-test

[mbed-ci]

Test : SUCCESS

Build number : 191
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/5395/191