drivers: remove unused build variable

The variable fmt_name has been removed from DPDK 21.02-rc1.
Then some drivers were integrated in the same year with this variable.
Of course it has no effect, so it is cleaned up.

Fixes: 832a4cf1d1 ("compress/mlx5: introduce PMD")
Fixes: a7c86884f1 ("crypto/mlx5: introduce Mellanox crypto driver")
Fixes: 5e7596ba7c ("vdpa/sfc: introduce Xilinx vDPA driver")
Cc: stable@dpdk.org

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>

drivers/compress/mlx5/meson.build

@@ -7,7 +7,6 @@ if not is_linux
     subdir_done()
 endif
 
-fmt_name = 'mlx5_compress'
 deps += ['common_mlx5', 'eal', 'compressdev']
 if not dpdk_conf.has('RTE_COMMON_MLX5')
     # avoid referencing undefined variables from common/mlx5

drivers/crypto/mlx5/meson.build

@@ -7,7 +7,6 @@ if not (is_linux or is_windows)
     subdir_done()
 endif
 
-fmt_name = 'mlx5_crypto'
 deps += ['common_mlx5', 'eal', 'cryptodev']
 if not dpdk_conf.has('RTE_COMMON_MLX5')
     # avoid referencing undefined variables from common/mlx5

drivers/vdpa/sfc/meson.build

@@ -8,7 +8,6 @@ if ((arch_subdir != 'x86' or not dpdk_conf.get('RTE_ARCH_64')) and
     reason = 'only supported on x86_64 and aarch64'
 endif
 
-fmt_name = 'sfc_vdpa'
 extra_flags = []
 
 foreach flag: extra_flags