Remove unused cmsis includes.

[tkem]

Description

Remove unused "cmsis.h" includes from CAN and TimerEvent drivers.
AFAICS those files do not use any CMSIS functionality, and I guess code in "drivers" shouldn't use CMSIS directly, anyway.
Since this is not really a "Fix" (nothing's broken, actually), I'll go with "Refactor" as Pull request type (maybe you want to add "Cleanup" to that list).

Pull request type

[ ] Fix
[x] Refactor
[ ] Target update
[ ] Functionality change
[ ] Breaking change

[cmonr]

@c1728p9 Could you take a quick look at this?

[cmonr]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 2931
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7891/

Triggering tests

/morph test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : FAILURE

Build number : 2549
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7891/

[0xc0170]

@OPpuolitaival @studavekar Another multiple defined symbols (cleanup problem?)

/morph export-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 2556
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7891/

[mbed-ci]

Test : SUCCESS

Build number : 2680
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7891/2680

[0xc0170]

/morph mbed2-build