meson: Remove triple-quoted strings

Triple-quoted strings are for multiline strings in Meson. None of the
descriptions that got changed were multiline and the entire file uses
single-line descriptions.

Author: Tristan Partin <tristan@neon.tech>
Discussion: https://www.postgresql.org/message-id/flat/CSPIJVUDZFKX.3KHMOAVGF94RV%40c3po

meson_options.txt

@@ -10,19 +10,19 @@ option('blocksize', type : 'combo',
 option('wal_blocksize', type : 'combo',
   choices: ['1', '2', '4', '8', '16', '32', '64'],
   value: '8',
-  description : '''WAL block size, in kilobytes''')
+  description : 'WAL block size, in kilobytes')
 
 option('segsize', type : 'integer', value : 1,
-  description : '''Segment size, in gigabytes''')
+  description : 'Segment size, in gigabytes')
 
 option('segsize_blocks', type : 'integer', value: 0,
-  description : '''Segment size, in blocks''')
+  description : 'Segment size, in blocks')
 
 
 # Miscellaneous options
 
 option('krb_srvnam', type : 'string', value : 'postgres',
-  description : '''Default Kerberos service principal for GSSAPI''')
+  description : 'Default Kerberos service principal for GSSAPI')
 
 option('system_tzdata', type: 'string', value: '',
   description: 'use system time zone data in specified directory')
@@ -32,7 +32,7 @@ option('system_tzdata', type: 'string', value: '',
 
 option('pgport', type : 'integer', value : 5432,
   min: 1, max: 65535,
-  description : '''Default port number for server and clients''')
+  description : 'Default port number for server and clients')
 
 
 # Developer options