Remove timestamp and PID from Android log format

[mhsmith]

This information is rarely helpful, and the added line length makes the log difficult to follow even in a moderately wide terminal.

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[freakboy3742]

A possible follow up that occurred to me: using a -v switch to control the amount of logging information that is displayed. For most day-to-day Toga apps, you really only care about I/python.stdout. Controlling the log filter to only show those lines and filter the tag prefix would give a very clean day-to-day log output; but if you turn on -v, you get all the other log lines plus the log prefix (and -vv turns on all the logs, including the ones that we're currently supressing).