gcov: remove support for GCC < 4.9

Since commit 0bddd22 ("Documentation: update for gcc 4.9
requirement") the minimum supported version of GCC is gcc-4.9.  It's now
safe to remove this code.

Similar to commit 1041553 ("gcov: Remove old GCC 3.4 support") but
that was for GCC 4.8 and this is for GCC 4.9.

Link: ClangBuiltLinux#427
Link: https://lkml.kernel.org/r/20201111030557.2015680-1-ndesaulniers@google.com
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/gcov/gcc_4_7.c

@@ -25,10 +25,8 @@
 #define GCOV_COUNTERS			9
 #elif (__GNUC__ > 5) || (__GNUC__ == 5 && __GNUC_MINOR__ >= 1)
 #define GCOV_COUNTERS			10
-#elif __GNUC__ == 4 && __GNUC_MINOR__ >= 9
-#define GCOV_COUNTERS			9
 #else
-#define GCOV_COUNTERS			8
+#define GCOV_COUNTERS			9
 #endif
 
 #define GCOV_TAG_FUNCTION_LENGTH	3