targets/*.conf cleanup: remove unnecessary TPUDRV_blob= lines MAIN_blob= and/or TPUDRV_blob= may be *optionally* defined in targets/*.conf files; if either variable is defined, it means that using the specified version of the blob library is allowed on this target, albeit likely suboptimal; if the variable is not defined, then using a blob is not an option and compilation from source is required for this component. MAIN_blob= and TPUDRV_blob= are now defaulted to empty in configure.sh, thus there is no need to explicitly specify that using a blob is not a valid option.

clean:	FRC
	rm -f fwimage.* ramimage.* str2ind.obj link.cmd link_ram.cmd
	rm -f build_date.* flash-script
	for i in ${SUBDIR}; do (cd $$i; ${MAKE} ${MFLAGS} clean); done