perf build: Remove unused feature test target

llvm-version was removed in commit 56b11a21 ("perf bpf: Remove
support for embedding clang for compiling BPF events (-e foo.c)") but
some parts were left in the Makefile so finish removing them.

Signed-off-by: James Clark <james.clark@linaro.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Bill Wendling <morbo@google.com>
Cc: Changbin Du <changbin.du@huawei.com>
Cc: Daniel Wagner <dwagner@suse.de>
Cc: Guilherme Amadio <amadio@gentoo.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Justin Stitt <justinstitt@google.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Leo Yan <leo.yan@arm.com>
Cc: Manu Bretelle <chantr4@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Monnet <qmo@kernel.org>
Cc: Steinar H. Gunderson <sesse@google.com>
Link: https://lore.kernel.org/r/20240910140405.568791-2-james.clark@linaro.org


[ Removed one leftover, 'llvm-version' from FEATURE_TESTS_EXTRA ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>