Cleanup: remove squid_DEPENDENCIES from Makefile

Cleanup: remove squid_DEPENDENCIES from Makefile

The bug *_DEPENDENCIES existed to solve no longer exists. Current auto*
toolchains can correctly generate the dependencies data based on *_LDADD
and *_SOURCES Makefile variables.

The incorrect definition of squid_DEPENDENCIES was also causing various
build issues and could result in crashes when conditionaly built features
were changed by users ./configure without a full re-bootstrap.

TODO: remove *_DEPENDEICIES for other binaries.