lint: always run module specified in ANDROID_LINT_CHECK_EXTRA_MODULES

Before this change, ANDROID_LINT_EXTRA_CHECK_MODULES was only read if
ANDROID_LINT_CHECK was also set.  This change allows an entire module of
checks to be added to lint without having to specify all of the
individuals with ANDROID_LINT_CHECK.

This is part of a workaround to run some lint checks globally, but is
useful to provide more flexibility generally.

Bug: 236558918
Test: manually tested with AndroidFrameworkLintChecker
Change-Id: I2d3ec8a997d902c9d00a577a56f4b152b10e078a