Do not add unnecessary prefix to dumpsys activity provider [NAME] --proto

Bug: 36904684
Test: builds, and tests succeed in the same topic branch

The test executes following
"dumpsys activity provider [launcher package name]/[provider name that implements workspace dump logging]
--proto"

In order to extract the proto binary from this stream, there cannot
be extra prefix added to each line. Hence, when "--proto" flag
is on, simply call the sub provider record's dump method.

This is following same pattern on other system service dump.
Having --proto flag also doesn't do any pretty printing.
e.g., dumpsys appwidget --proto.

Change-Id: I13712a45ce5b584123b3bd73c023df349fb86809