remove support for binutils 2.18 and 2.20

toolchain/binutils/Config.in

toolchain/binutils/Makefile

toolchain/binutils/patches/2.18/100-uclibc-conf.patch

toolchain/binutils/patches/2.18/110-arm-eabi-conf.patch

...binutils/patches/2.18/112-arm-uclibc-gas-needs-libm.patch

...ain/binutils/patches/2.18/300-001_ld_makefile_patch.patch

...ain/binutils/patches/2.18/300-006_better_file_error.patch

...inutils/patches/2.18/300-012_check_ldrunpath_length.patch

toolchain/binutils/patches/2.18/500-avr32.patch

toolchain/binutils/patches/2.18/601-cris-errormsg.patch

.../patches/2.18/700-pr5322-dont-adjust-p_vaddr_offset.patch

toolchain/binutils/patches/2.20/110-arm-eabi-conf.patch

toolchain/binutils/patches/2.20/111-pr7093.elf32-arm.c.patch

...binutils/patches/2.20/112-arm-uclibc-gas-needs-libm.patch

toolchain/binutils/patches/2.20/120-sh-conf.patch

toolchain/binutils/patches/2.20/200-mips_non_pic.patch

...ain/binutils/patches/2.20/300-001_ld_makefile_patch.patch

...inutils/patches/2.20/300-012_check_ldrunpath_length.patch