Makefile.am: fix warning in "make clean"
Makefile.am: fix warning in "make clean"

Remove invalid CLEANFILES directive, which should have been

CLEANFILES += doxygen-doc/*

but is already covered by DX_CLEANFILES. This fixes a non-fatal
error in "make clean-generic".

Fixes dd54f333f43860aaf9641873cb45c0808e9a3d8a.

Signed-off-by: Jonas Witschel <87a164e5d00d5dcdd001e37b34ea8bcd3fc3a172@gmx.de>

tpm2-software/tpm2-tss,01org/tpm2-tss,01org/TPM2.0-TSS,01org/tpm2-tss,01org/TPM2.0-TSS,01org/TPM2.0-TSS,01org/tpm2-tss,tpm2-software/tpm2-tss,01org/TPM2.0-TSS,tpm2-software/tpm2-tss