Drop compatibility definitions for R < 3.4

SET_GROWABLE_BIT appeared in 3.4.0, which we now depend upon.
R_(Calloc|Realloc|Free) seem to have existed for a long time and
definitely were available in 3.4 (per #6380).

Author: aitap

src/data.table.h

@@ -12,12 +12,6 @@
 #  define COMPLEX_RO COMPLEX
 #  define RAW_RO RAW
 #  define LOGICAL_RO LOGICAL
-#  define R_Calloc(x, y) Calloc(x, y)         // #6380
-#  define R_Realloc(x, y, z) Realloc(x, y, z)
-#  define R_Free(x) Free(x)
-#endif
-#if R_VERSION < R_Version(3, 4, 0)
-#  define SET_GROWABLE_BIT(x)  // #3292
 #endif
 // TODO: remove the `R_SVN_VERSION` check when R 4.5.0 is released (circa Apr. 2025)
 #if R_VERSION < R_Version(4, 5, 0) || R_SVN_REVISION < 86702