Exempt ARC/TV from enable_pip2_implementation flag

Per discussion, the enable_pip2_implementation will not force the
implementation choice on ARC and/or TV. ARC and TV can have their own
trunk stable flag when they start to adopt the new implementation.

See also go/pip-quality-plan

Bug: 311462191
Test: m -j
Change-Id: I2f5ab961e521565033786e9bdbc293b9901babe1