xzgrep.1: Delete superfluous '.PP'

Summary:

mandoc -T lint xzgrep.1 :
mandoc: xzgrep.1:79:2: WARNING: skipping paragraph macro: PP empty

  There is no change in the output of "nroff" and "troff".

Signed-off-by: Bjarni Ingi Gislason <bjarniig@rhi.hi.is>

src/scripts/xzgrep.1

@@ -76,7 +76,6 @@
 and
 .BR lzfgrep ,
 which are provided for backward compatibility with LZMA Utils.
-.PP
 .SH ENVIRONMENT
 .TP
 .B GREP