Remove the double blank line from source files

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

boards/z80/ez80/z20x/README.txt

@@ -11,7 +11,6 @@ README.txt
   exposure to technical details, the system also avoids using secondary
   MCUs or programmable logic, and sticks only with true hardware solutions.
 
-
  System Summary
 
     eZ80 running at 20 MHz (default on board)

boards/z80/z80/z80sim/README.txt

@@ -39,7 +39,6 @@ Configuring NuttX
     2) Make sure that your PATH environment variable includes the path
        to the SDCC toolchain.
 
-
     3) Then build the binaries:
 
           make
@@ -81,7 +80,6 @@ Configuring NuttX
     2) Set the PATH environment variable to include the path to the SDCC
        toolchain.
 
-
     3) Then build the binaries:
 
           make