package/librtlsdr: switch to autotools-package

Switch to autotools-package to avoid the following static build failure
since commit d6617402:

[ 56%] Linking C executable rtl_biast
/home/peko/autobuild/instance-1/output-1/host/opt/ext-toolchain/bin/../lib/gcc/riscv64-buildroot-linux-musl/10.3.0/../../../../riscv64-buildroot-linux-musl/bin/ld: attempted static link of dynamic object `/home/peko/autobuild/instance-1/output-1/host/riscv64-buildroot-linux-musl/sysroot/lib/libatomic.so'
collect2: error: ld returned 1 exit status

Drop both cmake-related patches

Fixes:
 - http://autobuild.buildroot.org/results/cf84759682848db8ed5610e1abe5a92337d0e957



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>