Fix doc of TOOL_TYPE_MOUSE.

It says it's set when the tool type is a mouse or trackpad, but the fact
is the tool type is TOOL_TYPE_FINGER on trackpads. Therefore remove
trackpad from Android doc.

Bug: 145135609
Test: N/A
Change-Id: Ife91ba032f9f0a8e7359425b415409ac609cdb25