Revert "Redefine QGA_READ_COUNT_DEFAULT as QCHANNEL_READ_COUNT_DEFAULT"

This reverts commit 5b58c35c064d7d13de9dea5ba28d52bc5488dd05.
Revert "Rename GAChannel to QChannel"

This reverts commit 3280b887ae920181a597c89fa65700147a52caa1.
Revert "Build GAChannel into libqemuutil"

This reverts commit 21589f9e053e2afc3941a011393020b3ae4286ca.