tpm2-tools: drop dependency on tpm2-abrmd

tpm2-tools is commonly used with the resource manager, tpm2-abrmd - But it
CAN be used without, E.G. by setting the TPM2TOOLS_TCTI_NAME environment
variable to communicate directly with the kernel driver:

export TPM2TOOLS_TCTI_NAME=device

Either directly with the TPM device (/dev/tpmN) or through the in-kernel
resource manager provided by Linux kernel since 4.12 (/dev/tpmrmN)

For some use cases (E.G. initramfs) it makes sense to use tpm2-tools
without abrmd, so remove the tpm2-abrmd select, and instead a note in the
help text that it may be needed.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>