INSTALL.md: Remove mention of md2man-roff
INSTALL.md: Remove mention of md2man-roff

md2man-roff is not needed (use Pandoc instead, which is already mentioned).

Fixes #1005.

Signed-off-by: Dan Anderson <8be6c5bcd7b3ecb36751de5a157aa00817bebea0@intel.com>

martinezjavier/tpm2-tools,martinezjavier/tpm2-tools,01org/tpm2.0-tools,martinezjavier/tpm2-tools,01org/tpm2.0-tools,martinezjavier/tpm2-tools,01org/tpm2.0-tools